UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Investment Company Act File Number: 811-04441

T. Rowe Price GNMA Fund

(Exact name of registrant as specified in charter)

100 East Pratt Street, Baltimore, MD 21202

(Address of principal executive offices)

David Oestreicher

100 East Pratt Street, Baltimore, MD 21202

(Name and address of agent for service)

Registrant’s telephone number, including area code: (410) 345-2000

Date of fiscal year end: May 31

Date of reporting period: November 30, 2015

The views and opinions in this report were current as of November 30, 2015. They are not guarantees of performance or investment results and should not be taken as investment advice. Investment decisions reflect a variety of factors, and the managers reserve the right to change their views about individual stocks, sectors, and the markets at any time. As a result, the views expressed should not be relied upon as a forecast of the fund’s future investment intent. The report is certified under the Sarbanes-Oxley Act, which requires mutual funds and other public companies to affirm that, to the best of their knowledge, the information in their financial reports is fairly and accurately stated in all material respects.

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The U.S. economy continued to grow amid increased concerns about a slowdown in some global economies. Intermediate- and long-term interest rates moved modestly higher over the course of the six-month reporting period while shorter rates saw a more significant increase. GNMAs and other agency mortgage-backed securities (MBS) outperformed most other fixed income sectors as they benefited from their relative insulation from the turbulence in international financial markets.

The GNMA Fund returned -0.03% over the six months ended November 30, 2015. As shown in the Performance Comparison table, the fund outperformed the Lipper GNMA Funds Average while lagging the Barclays U.S. GNMA Index.

The U.S. economy bounced back from a sluggish first quarter and grew at a moderate pace during our reporting period even as there were signs of a global slowdown. The U.S. economy expanded at a 2.1% annual rate in the third quarter of 2015, the Commerce Department reported at the end of November, which followed a 3.9% pace in the second quarter.

Other gauges also indicated a generally solid economic foundation. Nonfarm payrolls grew at an average monthly pace of 215,000 during the six-month period ending in October. The unemployment rate declined to 5.0%—its lowest level since the spring of 2008—versus the 5.4% jobless rate at the start of the reporting period, and wages showed some signs of accelerating. However, the labor force participation rate remained at historically low levels. Inflation was subdued and ran below the Fed’s 2% target over the past year amid tumbling crude oil prices and a stronger U.S. dollar, which reduces import prices.

The question of when the Federal Reserve would begin to raise short-term rates from near zero was a focus of bond markets throughout the year. In December, after our reporting period ended, Fed officials decided to raise short-term rates because of labor market improvement and their confidence that inflation will return to 2% over the medium term. Although the Fed ended outright purchases of MBS and Treasuries in October 2014, the central bank said it will continue to reinvest interest and principal payments from its MBS holdings back into the sector “until normalization of the level of the federal funds rate is well under way.”

The yield on the 10-year U.S. Treasury note—which best approximates the maturity of GNMAs and other MBS—finished modestly higher during our reporting period. Although there were some fluctuations in yields, volatility was relatively muted compared with earlier periods. Yields rose in June as concerns increased over the possibility of an imminent rate increase, and they then dipped to a low of just under 2% in October during a risk-averse environment that resulted from worries about a slowdown in global growth. The Fed’s October 28 statement, which pointed toward a rate increase by the end of the year, followed by a robust employment report caused another sell-off in Treasuries, and the 10-year yield finished November at 2.21%.

The relatively narrow trading range of 10-year Treasuries in comparison with previous months provided a supportive environment for agency MBS. These securities typically perform better during periods of lower market volatility because the risk of prepayment activity tends to decline. In addition, the weaker performance of other credit sectors during the last six months increased the attractiveness for investors of higher-quality and more liquid assets such as agency MBS.

Despite some lingering concerns in the market regarding potential Federal Housing Authority (FHA) underwriting changes that could lead to higher prepayment risk in the sector, GNMA-backed MBS performed slightly better than the broader agency MBS market as domestic bank and foreign investor demand for GNMA-issued MBS provided a supportive environment for the sector.

Our out-of-benchmark mortgage credit positions detracted from relative results during the period while security selection and sector allocation decisions were generally beneficial. We attempted to protect against some of the credit risk inherent in the commercial mortgage-backed securities (CMBS) holdings that we added during the period; however, the position hampered results.

Our overweight to 30-year maturities contributed to relative results, and our positioning in newly originated pools of mortgages proved particularly beneficial as a result of their generally better liquidity. Security selection in higher-coupon bonds also added value as our positioning in certain mortgage pools was positive and prepayments declined. Additionally, our preference for GNMA holdings over mortgages guaranteed by Fannie Mae and Freddie Mac (which are not government insured and are not included in our benchmark) contributed.

The liquidity and strong credit quality of agency MBS are key characteristics of this sector, which continues to draw support from fixed income investors. We structure the portfolio to provide shareholders with the most attractive risk-appropriate opportunities in the market; balancing the cost of liquidity against risk level is an integral part of our investment and risk-monitoring process. The management team also uses internally and externally developed quantitative tools to track and manage the risk profile of the portfolio as market conditions change.

Although our returns were slightly negative for the period in absolute terms, we were pleased that we were able to provide solid relative returns and outperform our Lipper peer group, and we believe the portfolio is well positioned to succeed in the rising-rate environment that we now appear to be entering.

Now that the first Fed rate hike is out of the way, Fed officials are likely to take some time assessing its impact on financial markets and economic conditions. Subsequent increases are likely to occur gradually, so the Fed may wait a few months before acting again, and the market expects only two or three rate hikes in 2016. The economic environment in the U.S. is likely to be positive. A number of factors will support U.S. households’ real disposable income, including cheap commodities, low interest rates, and gradually rising wages. U.S. fiscal policy also remains modestly supportive of growth, and the housing market looks set to strengthen, resulting in an estimated gross domestic product growth rate of 2.0% to 2.5% in 2016.

Our expectations are for MBS to perform better than riskier parts of the fixed income market as investors react to a less accommodative monetary policy. The income generated by our fund should provide shareholders with some protection against higher interest rates. GNMAs and the broader agency MBS market should continue to benefit from healthy demand for liquid bonds with high credit quality. Security selection is still critical, however, and we will continue to rely heavily on our extensive team of analysts, who provide careful, fundamental research on individual bonds.

The committee chairman has day-to-day responsibility for managing the portfolio and works with committee members in developing and executing the fund’s investment program.

Even though principal and interest payments on GNMAs are guaranteed, an increase in interest rates can cause the share price to decline, resulting in a loss of principal. Investors in bond funds are also subject to several other types of risk—interest rate risk, credit risk, prepayment risk, extension risk, and derivatives risk. Since the fund invests primarily in GNMAs, which are backed by the full faith and credit of the U.S. government, its exposure to credit risk is low. A mortgage-backed bond, unlike most other bonds, can be hurt when interest rates fall because homeowners tend to refinance and prepay principal. Prepayments can cause the average maturity of the portfolio to shorten, require the fund to reinvest proceeds at lower interest rates, or even cause certain bonds’ prices to fall below what the fund paid for them, resulting in a capital loss. Increased interest rates can cause the fund’s average maturity to lengthen unexpectedly due to a drop in mortgage prepayments. Shareholders are also exposed to derivatives risk, the potential that our investments in these complex and volatile instruments could affect the fund’s share price.

Asset-backed securities: Bonds whose payments are backed by a pool of receivables or other financial assets.

Barclays U.S. GNMA Index: Tracks the performance of mortgage-backed pass-through securities of the Government National Mortgage Association (GNMA).

Collateralized mortgage obligation: Bonds backed by mortgage pass-throughs whose cash flows are directed in different ways to different classes. Some classes may have less risk associated with prepayments, and, by default, the other classes will have more prepayment risk.

Commercial mortgage-backed securities (CMBS): Bonds backed by loans on commercial rather than residential properties.

Duration: A measure of a bond fund’s sensitivity to changes in interest rates. For example, a fund with a duration of five years would fall about 5% in price in response to a one-percentage-point rise in interest rates, and vice versa.

Federal funds rate: The interest rate charged on overnight loans of reserves by one financial institution to another in the U.S. The Federal Reserve sets a target federal funds rate to affect the level and direction of market rates.

Gross domestic product (GDP): The total market value of all goods and services produced in a country in a given year.

Lipper averages: The averages of available mutual fund performance returns for specified time periods in categories defined by Lipper Inc.

SEC yield (30-day): A method of calculating a fund’s yield that assumes all portfolio securities are held until maturity. Yield will vary and is not guaranteed.

Total return: The annual rate of return on a bond, taking into account interest income, plus appreciation or depreciation. If a bond is held to maturity, its total return equals its yield to maturity.

Weighted average maturity: A measure of a fund’s interest rate sensitivity. In general, the longer the average maturity, the greater the fund’s sensitivity to interest rate changes. The weighted average maturity may take into account the interest rate readjustment dates for certain securities. Money funds must maintain a weighted average maturity of less than 60 days.

Yield curve: A graphic depiction of the relationship between yields and maturity dates for a set of similar securities. A security with a longer maturity usually has a higher yield. If a short-term security offers a higher yield, then the curve is said to be “inverted.” If short- and long-term bonds are offering equivalent yields, then the curve is said to be “flat.”

This chart shows the value of a hypothetical $10,000 investment in the fund over the past 10 fiscal year periods or since inception (for funds lacking 10-year records). The result is compared with benchmarks, which may include a broad-based market index and a peer group average or index. Market indexes do not include expenses, which are deducted from fund returns as well as mutual fund averages and indexes.

As a mutual fund shareholder, you may incur two types of costs: (1) transaction costs, such as redemption fees or sales loads, and (2) ongoing costs, including management fees, distribution and service (12b-1) fees, and other fund expenses. The following example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds. The example is based on an investment of $1,000 invested at the beginning of the most recent six-month period and held for the entire period.

Actual Expenses
The first line of the following table (Actual) provides information about actual account values and expenses based on the fund’s actual returns. You may use the information on this line, together with your account balance, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number on the first line under the heading “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes
The information on the second line of the table (Hypothetical) is based on hypothetical account values and expenses derived from the fund’s actual expense ratio and an assumed 5% per year rate of return before expenses (not the fund’s actual return). You may compare the ongoing costs of investing in the fund with other funds by contrasting this 5% hypothetical example and the 5% hypothetical examples that appear in the shareholder reports of the other funds. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period.

Note: T. Rowe Price charges an annual account service fee of $20, generally for accounts with less than $10,000. The fee is waived for any investor whose T. Rowe Price mutual fund accounts total $50,000 or more; accounts electing to receive electronic delivery of account statements, transaction confirmations, prospectuses, and shareholder reports; or accounts of an investor who is a T. Rowe Price Preferred Services, Personal Services, or Enhanced Personal Services client (enrollment in these programs generally requires T. Rowe Price assets of at least $100,000). This fee is not included in the accompanying table. If you are subject to the fee, keep it in mind when you are estimating the ongoing expenses of investing in the fund and when comparing the expenses of this fund with other funds.

You should also be aware that the expenses shown in the table highlight only your ongoing costs and do not reflect any transaction costs, such as redemption fees or sales loads. Therefore, the second line of the table is useful in comparing ongoing costs only and will not help you determine the relative total costs of owning different funds. To the extent a fund charges transaction costs, however, the total cost of owning that fund is higher.

T. Rowe Price GNMA Fund (the fund), is registered under the Investment Company Act of 1940 (the 1940 Act) as a diversified, open-end management investment company. The fund commenced operations on November 26, 1985. The fund seeks high current income consistent with high overall credit quality and moderate price fluctuation by investing at least 80% of its total assets in Government National Mortgage Association securities backed by the full faith and credit of U.S. government.

Basis of Preparation The fund is an investment company and follows accounting and reporting guidance in the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946 (ASC 946). The accompanying financial statements were prepared in accordance with accounting principles generally accepted in the United States of America (GAAP), including, but not limited to, ASC 946. GAAP requires the use of estimates made by management. Management believes that estimates and valuations are appropriate; however, actual results may differ from those estimates, and the valuations reflected in the accompanying financial statements may differ from the value ultimately realized upon sale or maturity.

Investment Transactions, Investment Income, and Distributions Income and expenses are recorded on the accrual basis. Premiums and discounts on debt securities are amortized for financial reporting purposes. Paydown gains and losses are recorded as an adjustment to interest income. Dividends received from mutual fund investments are reflected as dividend income; capital gain distributions are reflected as realized gain/loss. Dividend income and capital gain distributions are recorded on the ex-dividend date. Income tax-related interest and penalties, if incurred, would be recorded as income tax expense. Investment transactions are accounted for on the trade date. Realized gains and losses are reported on the identified cost basis. Distributions to shareholders are recorded on the ex-dividend date. Income distributions are declared daily and paid monthly. Capital gain distributions, if any, are generally declared and paid by the fund annually.

New Accounting Guidance In May 2015, FASB issued ASU No. 2015-07, Fair Value Measurement (Topic 820), Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent). The ASU removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient and amends certain disclosure requirements for such investments. The ASU is effective for interim and annual reporting periods beginning after December 15, 2015. Adoption will have no effect on the fund’s net assets or results of operations.

The fund’s financial instruments are valued and its net asset value (NAV) per share is computed at the close of the New York Stock Exchange (NYSE), normally 4 p.m. ET, each day the NYSE is open for business.

Fair Value The fund’s financial instruments are reported at fair value, which GAAP defines as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The T. Rowe Price Valuation Committee (the Valuation Committee) has been established by the fund’s Board of Trustees (the Board) to ensure that financial instruments are appropriately priced at fair value in accordance with GAAP and the 1940 Act. Subject to oversight by the Board, the Valuation Committee develops and oversees pricing-related policies and procedures and approves all fair value determinations. Specifically, the Valuation Committee establishes procedures to value securities; determines pricing techniques, sources, and persons eligible to effect fair value pricing actions; oversees the selection, services, and performance of pricing vendors; oversees valuation-related business continuity practices; and provides guidance on internal controls and valuation-related matters. The Valuation Committee reports to the Board and has representation from legal, portfolio management and trading, operations, risk management, and the fund’s treasurer.

Various valuation techniques and inputs are used to determine the fair value of financial instruments. GAAP establishes the following fair value hierarchy that categorizes the inputs used to measure fair value:

Level 1 – quoted prices (unadjusted) in active markets for identical financial instruments that the fund can access at the reporting date

Level 2 – inputs other than Level 1 quoted prices that are observable, either directly or indirectly (including, but not limited to, quoted prices for similar financial instruments in active markets, quoted prices for identical or similar financial instruments in inactive markets, interest rates and yield curves, implied volatilities, and credit spreads)

Observable inputs are developed using market data, such as publicly available information about actual events or transactions, and reflect the assumptions that market participants would use to price the financial instrument. Unobservable inputs are those for which market data are not available and are developed using the best information available about the assumptions that market participants would use to price the financial instrument. GAAP requires valuation techniques to maximize the use of relevant observable inputs and minimize the use of unobservable inputs. When multiple inputs are used to derive fair value, the financial instrument is assigned to the level within the fair value hierarchy based on the lowest-level input that is significant to the fair value of the financial instrument. Input levels are not necessarily an indication of the risk or liquidity associated with financial instruments at that level but rather the degree of judgment used in determining those values.

Valuation Techniques Debt securities generally are traded in the over-the-counter (OTC) market. Securities with remaining maturities of one year or more at the time of acquisition are valued at prices furnished by dealers who make markets in such securities or by an independent pricing service, which considers the yield or price of bonds of comparable quality, coupon, maturity, and type, as well as prices quoted by dealers who make markets in such securities. Securities with remaining maturities of less than one year at the time of acquisition generally use amortized cost in local currency to approximate fair value. However, if amortized cost is deemed not to reflect fair value or the fund holds a significant amount of such securities with remaining maturities of more than 60 days, the securities are valued at prices furnished by dealers who make markets in such securities or by an independent pricing service. Generally, debt securities are categorized in Level 2 of the fair value hierarchy; however, to the extent the valuations include significant unobservable inputs, the securities would be categorized in Level 3.

Investments in mutual funds are valued at the mutual fund’s closing NAV per share on the day of valuation and are categorized in Level 1 of the fair value hierarchy. Financial futures contracts are valued at closing settlement prices and are categorized in Level 1 of the fair value hierarchy. Swaps are valued at prices furnished by independent swap dealers or by an independent pricing service and generally are categorized in Level 2 of the fair value hierarchy; however, if unobservable inputs are significant to the valuation, the swap would be categorized in Level 3. Assets and liabilities other than financial instruments, including short-term receivables and payables, are carried at cost, or estimated realizable value, if less, which approximates fair value.

Thinly traded financial instruments and those for which the above valuation procedures are inappropriate or are deemed not to reflect fair value are stated at fair value as determined in good faith by the Valuation Committee. The objective of any fair value pricing determination is to arrive at a price that could reasonably be expected from a current sale. Financial instruments fair valued by the Valuation Committee are primarily private placements, restricted securities, warrants, rights, and other securities that are not publicly traded.

Subject to oversight by the Board, the Valuation Committee regularly makes good faith judgments to establish and adjust the fair valuations of certain securities as events occur and circumstances warrant. For instance, in determining the fair value of troubled or thinly traded debt instruments, the Valuation Committee considers a variety of factors, which may include, but are not limited to, the issuer’s business prospects, its financial standing and performance, recent investment transactions in the issuer, strategic events affecting the company, market liquidity for the issuer, and general economic conditions and events. In consultation with the investment and pricing teams, the Valuation Committee will determine an appropriate valuation technique based on available information, which may include both observable and unobservable inputs. The Valuation Committee typically will afford greatest weight to actual prices in arm’s length transactions, to the extent they represent orderly transactions between market participants, transaction information can be reliably obtained, and prices are deemed representative of fair value. However, the Valuation Committee may also consider other valuation methods such as a discount or premium from market value of a similar, freely traded security of the same issuer; discounted cash flows; yield to maturity; or some combination. Fair value determinations are reviewed on a regular basis and updated as information becomes available, including actual purchase and sale transactions of the issue. Because any fair value determination involves a significant amount of judgment, there is a degree of subjectivity inherent in such pricing decisions, and fair value prices determined by the Valuation Committee could differ from those of other market participants. Depending on the relative significance of unobservable inputs, including the valuation technique(s) used, fair valued securities may be categorized in Level 2 or 3 of the fair value hierarchy.

Valuation Inputs The following table summarizes the fund’s financial instruments, based on the inputs used to determine their fair values on November 30, 2015:

There were no material transfers between Levels 1 and 2 during the six months ended November 30, 2015.

During the six months ended November 30, 2015, the fund invested in derivative instruments. As defined by GAAP, a derivative is a financial instrument whose value is derived from an underlying security price, foreign exchange rate, interest rate, index of prices or rates, or other variable; it requires little or no initial investment and permits or requires net settlement. The fund invests in derivatives only if the expected risks and rewards are consistent with its investment objectives, policies, and overall risk profile, as described in its prospectus and Statement of Additional Information. The fund may use derivatives for a variety of purposes, such as seeking to hedge against declines in principal value, increase yield, invest in an asset with greater efficiency and at a lower cost than is possible through direct investment, or to adjust portfolio duration and credit exposure. The risks associated with the use of derivatives are different from, and potentially much greater than, the risks associated with investing directly in the instruments on which the derivatives are based. The fund at all times maintains sufficient cash reserves, liquid assets, or other SEC-permitted asset types to cover its settlement obligations under open derivative contracts.

The fund values its derivatives at fair value, as described in Note 2, and recognizes changes in fair value currently in its results of operations. Accordingly, the fund does not follow hedge accounting, even for derivatives employed as economic hedges. Generally, the fund accounts for its derivatives on a gross basis. It does not offset the fair value of derivative liabilities against the fair value of derivative assets on its financial statements, nor does it offset the fair value of derivative instruments against the right to reclaim or obligation to return collateral. The following table summarizes the fair value of the fund’s derivative instruments held as of November 30, 2015, and the related location on the accompanying Statement of Assets and Liabilities, presented by primary underlying risk exposure:

Additionally, the amount of gains and losses on derivative instruments recognized in fund earnings during the six months ended November 30, 2015, and the related location on the accompanying Statement of Operations is summarized in the following table by primary underlying risk exposure:

Counterparty Risk and Collateral The fund invests in derivatives in various markets, which expose it to differing levels of counterparty risk. Counterparty risk on exchange-traded and centrally cleared derivative contracts, such as futures, exchange-traded options, and centrally cleared swaps, is minimal because the clearinghouse provides protection against counterparty defaults. For futures and centrally cleared swaps, the fund is required to deposit collateral in an amount equal to a certain percentage of the contract value (margin requirement), and the margin requirement must be maintained over the life of the contract. Each clearing broker, in its sole discretion, may adjust the margin requirements applicable to the fund.

Derivatives, such as bilateral swaps, forward currency exchange contracts, and OTC options, that are transacted and settle directly with a counterparty (bilateral derivatives) expose the fund to greater counterparty risk. To mitigate this risk, the fund has entered into master netting arrangements (MNAs) with certain counterparties that permit net settlement under specified conditions and, for certain counterparties, also provide collateral agreements. MNAs may be in the form of International Swaps and Derivatives Association master agreements (ISDAs) or foreign exchange letter agreements (FX letters).

MNAs govern the ability to offset amounts the fund owes a counterparty against amounts the counterparty owes the fund (net settlement). Both ISDAs and FX letters generally allow net settlement in the event of contract termination and permit termination by either party prior to maturity upon the occurrence of certain stated events, such as failure to pay or bankruptcy. In addition, ISDAs specify other events, the occurrence of which would allow one of the parties to terminate. For example, a downgrade in credit rating of a counterparty would allow the fund to terminate while a decline in the fund’s net assets of more than a certain percentage would allow the counterparty to terminate. Upon termination, all bilateral derivatives with that counterparty would be liquidated and a net amount settled. ISDAs typically include collateral agreements whereas FX letters do not. Collateral requirements are determined based on the net aggregate unrealized gain or loss on all bilateral derivatives with each counterparty, subject to minimum transfer amounts that typically range from $100,000 to $250,000. Any additional collateral required due to changes in security values is transferred the next business day.

Collateral may be in the form of cash or debt securities issued by the U.S. government or related agencies. Cash and currencies posted by the fund are reflected as cash deposits in the accompanying financial statements and generally are restricted from withdrawal by the fund; securities posted by the fund are so noted in the accompanying Portfolio of Investments; both remain in the fund’s assets. Collateral pledged by counterparties is not included in the fund’s assets because the fund does not obtain effective control over those assets. For bilateral derivatives, collateral posted or received by the fund is held in a segregated account by the fund’s custodian. As of November 30, 2015, no collateral had been posted by the fund to counterparties for bilateral derivatives. As of November 30, 2015, collateral pledged by counterparties to the fund for bilateral derivatives consisted of securities valued at $711,000. As of November 30, 2015, securities valued at $2,299,000 had been posted by the fund for exchange-traded and/or centrally cleared derivatives.

Futures Contracts The fund is subject to interest rate risk in the normal course of pursuing its investment objectives and uses futures contracts to help manage such risk. The fund may enter into futures contracts to manage exposure to interest rate and yield curve movements, security prices, foreign currencies, credit quality, and mortgage prepayments; as an efficient means of adjusting exposure to all or part of a target market; to enhance income; as a cash management tool; or to adjust portfolio duration and credit exposure. A futures contract provides for the future sale by one party and purchase by another of a specified amount of a specific underlying financial instrument at an agreed-upon price, date, time, and place. The fund currently invests only in exchange-traded futures, which generally are standardized as to maturity date, underlying financial instrument, and other contract terms. Payments are made or received by the fund each day to settle daily fluctuations in the value of the contract (variation margin), which reflect changes in the value of the underlying financial instrument. Variation margin is recorded as unrealized gain or loss until the contract is closed. The value of a futures contract included in net assets is the amount of unsettled variation margin; net variation margin receivable is reflected as an asset, and net variation margin payable is reflected as a liability on the accompanying Statement of Assets and Liabilities. Risks related to the use of futures contracts include possible illiquidity of the futures markets, contract prices that can be highly volatile and imperfectly correlated to movements in hedged security values and/or interest rates, and potential losses in excess of the fund’s initial investment. During the six months ended November 30, 2015, the volume of the fund’s activity in futures, based on underlying notional amounts, was generally between 6% and 21% of net assets.

Swaps The fund is subject to credit risk in the normal course of pursuing its investment objectives and uses swap contracts to help manage such risk. The fund may use swaps in an effort to manage exposure to changes in interest rates, inflation rates, and credit quality; to adjust overall exposure to certain markets; to enhance total return or protect the value of portfolio securities; to serve as a cash management tool; or to adjust portfolio duration and credit exposure. Swap agreements can be settled either directly with the counterparty (bilateral swap) or through a central clearinghouse (centrally cleared swap). Fluctuations in the fair value of a contract are reflected in unrealized gain or loss and are reclassified to realized gain or loss upon contract termination or cash settlement. Net periodic receipts or payments required by a contract increase or decrease, respectively, the value of the contract until the contractual payment date, at which time such amounts are reclassified from unrealized to realized gain or loss. For bilateral swaps, cash payments are made or received by the fund on a periodic basis in accordance with contract terms; unrealized gain on contracts and premiums paid are reflected as assets and unrealized loss on contracts and premiums received are reflected as liabilities on the accompanying Statement of Assets and Liabilities. For centrally cleared swaps, payments are made or received by the fund each day to settle the daily fluctuation in the value of the contract (variation margin). Accordingly, the value of a centrally cleared swap included in net assets is the unsettled variation margin; net variation margin receivable is reflected as an asset and net variation margin payable is reflected as a liability on the accompanying Statement of Assets and Liabilities.

Credit default swaps are agreements where one party (the protection buyer) agrees to make periodic payments to another party (the protection seller) in exchange for protection against specified credit events, such as certain defaults and bankruptcies related to an underlying credit instrument, or issuer or index of such instruments. Upon occurrence of a specified credit event, the protection seller is required to pay the buyer the difference between the notional amount of the swap and the value of the underlying credit, either in the form of a net cash settlement or by paying the gross notional amount and accepting delivery of the relevant underlying credit. For credit default swaps where the underlying credit is an index, a specified credit event may affect all or individual underlying securities included in the index and will be settled based upon the relative weighting of the affected underlying security(ies) within the index. Risks related to the use of credit default swaps include the possible inability of the fund to accurately assess the current and future creditworthiness of underlying issuers, the possible failure of a counterparty to perform in accordance with the terms of the swap agreements, potential government regulation that could adversely affect the fund’s swap investments, and potential losses in excess of the fund’s initial investment.

During the six months ended November 30, 2015, the volume of the fund’s activity in swaps, based on underlying notional amounts, was generally between 0% and 2% of net assets.

Consistent with its investment objective, the fund engages in the following practices to manage exposure to certain risks and/or to enhance performance. The investment objective, policies, program, and risk factors of the fund are described more fully in the fund’s prospectus and Statement of Additional Information.

Restricted Securities The fund may invest in securities that are subject to legal or contractual restrictions on resale. Prompt sale of such securities at an acceptable price may be difficult and may involve substantial delays and additional costs.

TBA Purchase and Sale Commitments The fund may enter into to-be-announced (TBA) purchase or sale commitments, pursuant to which it agrees to purchase or sell, respectively, mortgage-backed securities for a fixed unit price, with payment and delivery at a scheduled future date beyond the customary settlement period for such securities. With TBA transactions, the particular securities to be delivered are not identified at the trade date; however, delivered securities must meet specified terms, including issuer, rate, and mortgage term, and be within industry-accepted “good delivery” standards. The fund may enter into TBA purchase transactions with the intention of taking possession of the underlying securities, may elect to extend the settlement by “rolling” the transaction, and/or may use TBAs to gain interim exposure to underlying securities. Until settlement, the fund maintains liquid assets sufficient to settle its TBA commitments.

To mitigate counterparty risk, the fund has entered into agreements with TBA counterparties that provide for collateral and the right to offset amounts due to or from those counterparties under specified conditions. Subject to minimum transfer amounts, collateral requirements are determined and transfers made based on the net aggregate unrealized gain or loss on all TBA commitments with a particular counterparty. At any time, the fund’s risk of loss from a particular counterparty related to its TBA commitments is the aggregate unrealized gain on appreciated TBAs in excess of unrealized loss on depreciated TBAs and collateral received, if any, from such counterparty. As of November 30, 2015, cash of $99,000 had been posted by the fund to counterparties for TBAs. Collateral pledged by counterparties to the fund for TBAs consisted of $6,000 cash and securities valued at $152,000 as of November 30, 2015.

Dollar Rolls The fund may enter into dollar roll transactions, pursuant to which it sells a mortgage-backed TBA or security and simultaneously agrees to purchase a similar, but not identical, TBA with the same issuer, rate, and terms on a later date at a set price from the same counterparty. The fund may execute a “roll” to obtain better underlying mortgage securities or to enhance returns. The fund generally enters into dollar roll transactions with the intention of taking possession of the underlying mortgage securities but may close a contract prior to settlement or “roll” settlement to a later date if deemed to be in the best interest of shareholders. Actual mortgages received by the fund may be less favorable than those anticipated. The fund accounts for dollar roll transactions as purchases and sales, which has the effect of increasing its portfolio turnover rate.

Mortgage-Backed Securities The fund may invest in mortgage-backed securities (MBS or pass-through certificates) that represent an interest in a pool of specific underlying mortgage loans and entitle the fund to the periodic payments of principal and interest from those mortgages. MBS may be issued by government agencies or corporations, or private issuers. Most MBS issued by government agencies are guaranteed; however, the degree of protection differs based on the issuer. The fund also may invest in stripped MBS, created when a traditional MBS is split into an interest-only (IO) and a principal-only (PO) strip. MBS, including IOs and POs, are sensitive to changes in economic conditions that affect the rate of prepayments and defaults on the underlying mortgages; accordingly, the value, income, and related cash flows from MBS may be more volatile than other debt instruments. IOs also risk loss of invested principal from faster-than-anticipated prepayments.

Other Purchases and sales of portfolio securities other than short-term and U.S. government securities aggregated $110,478,000 and $11,025,000, respectively, for the six months ended November 30, 2015. Purchases and sales of U.S. government securities aggregated $3,513,822,000 and $3,531,505,000, respectively, for the six months ended November 30, 2015.

No provision for federal income taxes is required since the fund intends to continue to qualify as a regulated investment company under Subchapter M of the Internal Revenue Code and distribute to shareholders all of its taxable income and gains. Distributions determined in accordance with federal income tax regulations may differ in amount or character from net investment income and realized gains for financial reporting purposes. Financial reporting records are adjusted for permanent book/tax differences to reflect tax character but are not adjusted for temporary differences. The amount and character of tax-basis distributions and composition of net assets are finalized at fiscal year-end; accordingly, tax-basis balances have not been determined as of the date of this report.

The fund intends to retain realized gains to the extent of available capital loss carryforwards. Net realized capital losses may be carried forward indefinitely to offset future realized capital gains. As of May 31, 2015, the fund had $49,129,000 of available capital loss carryforwards. Further, $5,981,000 of the fund’s available capital loss carryforwards acquired through tax-free reorganizations may be subject to certain limitations on amount or timing of use.

At November 30, 2015, the cost of investments for federal income tax purposes was $1,839,813,000. Net unrealized gain aggregated $8,869,000 at period-end, of which $26,571,000 related to appreciated investments and $17,702,000 related to depreciated investments.

The fund is managed by T. Rowe Price Associates, Inc. (Price Associates), a wholly owned subsidiary of T. Rowe Price Group, Inc. (Price Group). The investment management agreement between the fund and Price Associates provides for an annual investment management fee, which is computed daily and paid monthly. The fee consists of an individual fund fee, equal to 0.15% of the fund’s average daily net assets, and a group fee. The group fee rate is calculated based on the combined net assets of certain mutual funds sponsored by Price Associates (the group) applied to a graduated fee schedule, with rates ranging from 0.48% for the first $1 billion of assets to 0.275% for assets in excess of $400 billion. The fund’s group fee is determined by applying the group fee rate to the fund’s average daily net assets. At November 30, 2015, the effective annual group fee rate was 0.29%.

In addition, the fund has entered into service agreements with Price Associates and two wholly owned subsidiaries of Price Associates (collectively, Price). Price Associates provides certain accounting and administrative services to the fund. T. Rowe Price Services, Inc., provides shareholder and administrative services in its capacity as the fund’s transfer and dividend-disbursing agent. T. Rowe Price Retirement Plan Services, Inc., provides subaccounting and recordkeeping services for certain retirement accounts invested in the fund. For the six months ended November 30, 2015, expenses incurred pursuant to these service agreements were $38,000 for Price Associates; $312,000 for T. Rowe Price Services, Inc.; and $82,000 for T. Rowe Price Retirement Plan Services, Inc. The total amount payable at period-end pursuant to these service agreements is reflected as Due to Affiliates in the accompanying financial statements.

The fund is also one of several mutual funds sponsored by Price Associates (underlying Price funds) in which the T. Rowe Price Spectrum Funds (Spectrum Funds) may invest. The Spectrum Funds do not invest in the underlying Price funds for the purpose of exercising management or control. Pursuant to a special servicing agreement, expenses associated with the operation of the Spectrum Funds are borne by each underlying Price fund to the extent of estimated savings to it and in proportion to the average daily value of its shares owned by the Spectrum Funds. Expenses allocated under this agreement are reflected as shareholder servicing expense in the accompanying financial statements. For the six months ended November 30, 2015, the fund was allocated $386,000 of Spectrum Funds’ expenses, of which $262,000 related to services provided by Price. At period-end, the amount payable to Price pursuant to this agreement is reflected as Due to Affiliates in the accompanying financial statements. At November 30, 2015, approximately 37% of the outstanding shares of the fund were held by the Spectrum Funds.

The fund may invest in the T. Rowe Price Reserve Investment Fund, the T. Rowe Price Government Reserve Investment Fund, or the T. Rowe Price Short-Term Reserve Fund (collectively, the Price Reserve Investment Funds), open-end management investment companies managed by Price Associates and considered affiliates of the fund. The Price Reserve Investment Funds are offered as short-term investment options to mutual funds, trusts, and other accounts managed by Price Associates or its affiliates and are not available for direct purchase by members of the public. The Price Reserve Investment Funds pay no investment management fees.

A description of the policies and procedures used by T. Rowe Price funds and portfolios to determine how to vote proxies relating to portfolio securities is available in each fund’s Statement of Additional Information. You may request this document by calling 1-800-225-5132 or by accessing the SEC’s website, sec.gov.

The description of our proxy voting policies and procedures is also available on our website, troweprice.com. To access it, click on the words “Social Responsibility” at the top of our corporate homepage. Next, click on the words “Conducting Business Responsibly” on the left side of the page that appears. Finally, click on the words “Proxy Voting Policies” on the left side of the page that appears.

Each fund’s most recent annual proxy voting record is available on our website and through the SEC’s website. To access it through our website, follow the above directions to reach the “Conducting Business Responsibly” page. Click on the words “Proxy Voting Records” on the left side of that page, and then click on the “View Proxy Voting Records” link at the bottom of the page that appears.

The fund files a complete schedule of portfolio holdings with the Securities and Exchange Commission for the first and third quarters of each fiscal year on Form N-Q. The fund’s Form N-Q is available electronically on the SEC’s website (sec.gov); hard copies may be reviewed and copied at the SEC’s Public Reference Room, 100 F St. N.E., Washington, DC 20549. For more information on the Public Reference Room, call 1-800-SEC-0330.

A code of ethics, as defined in Item 2 of Form N-CSR, applicable to its principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions is filed as an exhibit to the registrant’s annual Form N-CSR. No substantive amendments were approved or waivers were granted to this code of ethics during the registrant’s most recent fiscal half-year.

(a) Not applicable. The complete schedule of investments is included in Item 1 of this Form N-CSR.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies.

Item 9. Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers.

(a) The registrant’s principal executive officer and principal financial officer have evaluated the registrant’s disclosure controls and procedures within 90 days of this filing and have concluded that the registrant’s disclosure controls and procedures were effective, as of that date, in ensuring that information required to be disclosed by the registrant in this Form N-CSR was recorded, processed, summarized, and reported timely.

(b) The registrant’s principal executive officer and principal financial officer are aware of no change in the registrant’s internal control over financial reporting that occurred during the registrant’s second fiscal quarter covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting.

(a)(1) The registrant’s code of ethics pursuant to Item 2 of Form N-CSR is filed with the registrant’s annual Form N-CSR.

(2) Separate certifications by the registrant's principal executive officer and principal financial officer, pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 and required by Rule 30a-2(a) under the Investment Company Act of 1940, are attached.

(3) Written solicitation to repurchase securities issued by closed-end companies: not applicable.

(b) A certification by the registrant's principal executive officer and principal financial officer, pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 and required by Rule 30a-2(b) under the Investment Company Act of 1940, is attached.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

T. Rowe Price GNMA Fund

	By	/s/ Edward C. Bernard
		Edward C. Bernard
		Principal Executive Officer

Date January 19, 2016

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

	By	/s/ Edward C. Bernard
		Edward C. Bernard
		Principal Executive Officer

Date January 19, 2016


	By	/s/ Catherine D. Mathews
		Catherine D. Mathews
		Principal Financial Officer

Date January 19, 2016