BlackRock California Municipal Series Trust

BlackRock California Municipal Opportunities Fund

BlackRock Municipal Bond Fund, Inc.

BlackRock High Yield Municipal Fund

BlackRock National Municipal Fund

BlackRock Multi-State Municipal Series Trust

BlackRock New Jersey Municipal Bond Fund

BlackRock New York Municipal Opportunities Fund

BlackRock Pennsylvania Municipal Bond Fund

BlackRock Municipal Series Trust

BlackRock Strategic Municipal Opportunities Fund

(each, a “Fund” and collectively, the “Funds”)

Supplement dated May 22, 2015 to the

Statement of Additional Information of each Fund

Effective immediately, Part II of each Fund’s Statement of Additional Information is amended as follows:

The section entitled “Investment Risks and Considerations—Municipal Investments—Tender Option Bonds” in Part II of each Fund’s current Statement of Additional Information is deleted in its entirety and replaced with the following:

Tender Option Bonds. Certain Funds may invest in residual inverse floating rate interest tender option bonds (“TOB Residuals”), which are derivative interests in Municipal Bonds. The TOB Residuals in which the Funds will invest pay interest or income that, in the opinion of counsel to the issuer, is exempt from regular Federal income tax. BlackRock will not conduct its own analysis of the tax status of the interest or income paid by TOB Residuals held by the Funds, but will rely on the opinion of counsel to the issuer. Although volatile, TOB Residuals typically offer the potential for yields exceeding the yields available on fixed rate Municipal Bonds with comparable credit quality. The Funds may invest in TOB Residuals for the purpose of using economic leverage.

TOB Residuals represent beneficial interests in a special purpose trust formed for the purpose of holding Municipal Bonds contributed by one or more funds (a “TOB Trust”). A TOB Trust typically issues two classes of beneficial interests: short-term floating rate interests (“TOB Floaters”), which are sold to third party investors, and TOB Residuals, which are generally issued to the fund(s) that transferred Municipal Bonds to the TOB Trust. The Funds may invest in both TOB Floaters and TOB Residuals. TOB Floaters may have first priority on the cash flow from the Municipal Bonds held by the TOB Trust and are enhanced with a liquidity support arrangement from a third party Liquidity Provider (defined below) which allows holders to tender their position at par (plus accrued interest). A Fund, as a holder of TOB Residuals, is paid the residual cash flow from the TOB Trust. A Fund that contributes the Municipal Bonds to the TOB Trust is paid the cash received by the TOB Trust from the sale of the TOB Floaters, less certain transaction costs, and typically will invest the cash to purchase additional Municipal Bonds or other investments permitted by its investment policies. If a Fund ever purchases all or a portion of the TOB Floaters sold by the TOB Trust, it may surrender those TOB Floaters together with a proportionate amount of TOB Residuals to the TOB Trust in exchange for a proportionate amount of the Municipal Bonds owned by the TOB Trust.

Other BlackRock-advised funds may contribute Municipal Bonds to a TOB Trust into which a Fund has contributed Municipal Bonds. If multiple BlackRock-advised funds participate in the same TOB Trust, the economic rights and obligations under the TOB Residual will generally be shared among the funds ratably in proportion to their participation in the TOB Trust.

The Municipal Bonds transferred to a TOB Trust typically are high grade Municipal Bonds. In certain cases, when Municipal Bonds transferred are lower grade Municipal Bonds, the TOB Trust transaction includes a credit enhancement feature that provides for the timely payment of principal and interest on the bonds to the TOB Trust by a credit enhancement provider. The TOB Trust would be responsible for the payment of the credit enhancement fee and a Fund, as a TOB Residual holder, would be responsible for reimbursement of any payments of principal and interest made by the credit enhancement provider.

The TOB Residuals held by a Fund generally provide the Fund with the right to cause the holders of a proportional share of the TOB Floaters to tender their notes to the TOB Trust at par plus accrued interest. Thereafter, the Fund may withdraw a corresponding share of the Municipal Bonds from the TOB Trust. This transaction, in effect, creates exposure for the Fund to the entire return of the Municipal Bonds in the TOB Trust, with a net cash investment by the Fund that is less than the value of the Municipal Bonds in the TOB Trust. This multiplies the positive or negative impact of the Municipal Bonds’ return within the Fund (thereby creating leverage). The leverage within a TOB Trust depends on the value of the Municipal Bonds deposited in the TOB Trust relative to the value of the TOB Floaters it issues.

A Fund may invest in highly leveraged TOB Residuals. A TOB Residual generally is considered highly leveraged if the principal amount of the TOB Floaters issued by the related TOB Trust exceeds 75% of the principal amount of the Municipal Bonds owned by the TOB Trust.

The TOB Trust may be collapsed without the consent of a Fund upon the occurrence of tender option termination events (“TOTEs”) and mandatory termination events (“MTEs”), as defined in the TOB Trust agreements. TOTEs include the bankruptcy or default of the issuer of the Municipal Bonds held in the TOB Trust, a substantial downgrade in the credit quality of the issuer of the Municipal Bonds held in the TOB Trust, failure of any scheduled payment of principal or interest on the Municipal Bonds, and a judgment or ruling that interest on the Municipal Bonds is subject to federal income taxation. MTEs may include, among other things, a failed remarketing of the TOB Floaters, the inability of the TOB Trust to obtain renewal of the liquidity support agreement, and a substantial decline in the market value of the Municipal Bonds held in the TOB Trust. Upon the occurrence of a TOTE or an MTE, a TOB Trust would be liquidated with the proceeds applied first to any accrued fees owed to the trustee of the TOB Trust, the remarketing agent of the TOB Floaters and the Liquidity Provider (defined below). In the case of an MTE, after the payment of fees, the holders of the TOB Floaters would be paid senior to the TOB Residual holders (i.e., the Fund). In contrast, in the case of a TOTE, after payment of fees, the holders of TOB Floaters and the TOB Residual holders would be paid pro rata in proportion to the respective face values of their certificates.

A Fund may invest in a TOB Trust on either a non-recourse and recourse basis. TOB Trusts are typically supported by a liquidity facility provided by a third-party bank or other financial institution (the “Liquidity Provider”) that allows the holders of the TOB Floaters to tender their TOB Floaters in exchange for payment of par plus accrued interest on any business day (subject to the non-occurrence of a TOTE described above). Depending on the structure of the TOB Trust, the Liquidity Provider may purchase the tendered TOB Floaters, or the TOB Trust may draw upon a loan from the Liquidity Provider to purchase the tendered TOB Floaters.

When a Fund invests in TOB Trusts on a non-recourse basis, and the Liquidity Provider is required to make a payment under the liquidity facility, the Liquidity Provider will typically liquidate all or a portion of the Municipal Bonds held in the TOB Trust and then fund the balance, if any, of the amount owed under the liquidity facility over the liquidation proceeds (the “Liquidation Shortfall”). If a Fund invests in a TOB Trust on a recourse basis, it will typically enter into a reimbursement agreement with the Liquidity Provider pursuant to which the Fund is required to reimburse the Liquidity Provider the amount of any Liquidation Shortfall. As a result, if the Fund invests in a recourse TOB Trust, the Fund will bear the risk of loss with respect to any Liquidation Shortfall. If multiple BlackRock-advised funds participate in any such TOB Trust, these losses will be shared ratably, in proportion to their participation in the TOB Trust.

Under accounting rules, Municipal Bonds of a Fund that are deposited into a TOB Trust are investments of the Fund and are presented on the Fund’s Schedule of Investments and outstanding TOB Floaters issued by a TOB Trust are presented as liabilities in the Fund’s Statement of Assets and Liabilities. Interest income from the underlying Municipal Bonds is recorded by a Fund on an accrual basis. Interest expense incurred on the TOB Floaters and other expenses related to remarketing, administration, trustee and other services to a TOB Trust are reported as expenses of a Fund. In addition, under accounting rules, loans made to a TOB Trust sponsored by a Fund may be presented as loans of the Fund in the Fund’s financial statements even if there is no recourse to the Fund’s assets.

For TOB Floaters, generally, the interest rate earned will be based upon the market rates for Municipal Bonds with maturities or remarketing provisions that are comparable in duration to the periodic interval of the tender option. Since the tender option feature has a shorter term than the final maturity or first call date of the

underlying Municipal Bonds deposited in the TOB Trust, the holder of the TOB Floaters relies upon the terms of the agreement with the financial institution furnishing the liquidity facility as well as the credit strength of that institution. The risk associated with TOB Floaters, however, may be increased in the current market environment as a result of recent downgrades to the credit ratings, and thus the perceived reliability and creditworthiness, of many major financial institutions, some of which sponsor and/or provide liquidity support to TOB Trusts. This in turn may reduce the desirability of TOB Floaters as investments, which could impair the viability or availability of TOB Trusts.

The use of TOB Residuals will require the Fund to earmark or segregate liquid assets in an amount equal to any TOB Floaters, plus any accrued but unpaid interest due on the TOB Floaters, issued by TOB Trusts sponsored by, or on behalf of, the Fund that are not owned by the Fund. The use of TOB Residuals may also require the Fund to earmark or segregate liquid assets in an amount equal to loans provided by the Liquidity Provider to the TOB Trust to purchase tendered TOB Floaters. The Fund reserves the right to modify its asset segregation policies in the future to the extent that such changes are in accordance with applicable regulations or interpretations. Future regulatory requirements or SEC guidance may necessitate more onerous contractual or regulatory requirements, which may increase the costs or reduce the degree of potential economic benefits of TOB Trust transactions or limit the Fund’s ability to enter into or manage TOB Trust transactions.

Recent Developments in the TOB Trust Market. On December 10, 2013, regulators published final rules implementing section 619 of the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Volcker Rule”), which prohibit banking entities from engaging in proprietary trading of certain instruments and limit such entities’ investments in, and relationships with, “covered funds”, as defined in the Volcker Rule. The Volcker Rule precludes banking entities and their affiliates from sponsoring TOB Trusts as such Trusts have been structured prior to the effective date of the Volcker Rule. Banking entities subject to the Volcker Rule are required to fully comply by July 21, 2015, with respect to investments in and relationships with TOB Trusts that were not in place prior to December 31, 2013, and by July 21, 2016, with respect to investments in and relationships with TOB Trusts that were in place prior to December 31, 2013. As a result, TOB Trusts may need to be restructured or unwound.

In response to the restrictions imposed by the Volcker Rule, market participants have developed a new structure for TOB Trusts designed to ensure that no banking entity is sponsoring the TOB Trust for purposes of the Volcker Rule. Specifically, a Fund will establish, structure and “sponsor” the TOB Trusts in which it holds TOB Residuals. In such a structure, certain responsibilities that previously belonged to the sponsor bank will be performed by, or on behalf of, a Fund. A Fund may utilize service providers in meeting these responsibilities. This structure remains untested. It is possible that regulators could take positions that could limit the market for such newly structured TOB Trust transactions or a Fund’s ability to hold TOB Residuals. Under the new TOB Trust structure, a Fund will have certain additional duties and responsibilities, which may give rise to certain additional risks including, but not limited to, compliance, securities law and operational risks.

Service providers to a TOB Trust, such as administrators, liquidity providers, trustees, and remarketing agents, would be acting at the direction of, and as agent of, the Fund as the TOB Residual holder. Similar to the current tender option bond structure, a Fund would deposit Municipal Bonds into the TOB Trust in exchange for TOB Residuals, the TOB Trust would then issue and sell TOB Floaters to third party investors, and the proceeds of the sale of the TOB Floaters would be distributed to such TOB Residual holders (i.e., the Fund). Tendered TOB Floaters would continue to be supported by a remarketing agent and a liquidity facility. However, the remarketing agent is not anticipated to purchase tendered TOB Floaters for its own account in the event of a failed remarketing, which may increase the likelihood that a TOB Trust will need to be collapsed and liquidated in order to purchase the tendered TOB Floaters. In the event of a failed remarketing of TOB Floaters, the Liquidity Provider, at its option, may advance a loan to the TOB Trust the proceeds of which would be used by the TOB Trust to purchase the tendered TOB Floaters. The Liquidity Provider is not obligated to advance such a loan. The TOB Trust would be the borrower with respect to any such loan. Any loans made by a Liquidity Provider will be secured by the purchased TOB Floaters held by the TOB Trust.

Similar to the current structure for TOB Trusts, a Fund may hold either non-recourse TOB Residuals or recourse TOB Residuals under the new structure. In the event of a Liquidation Shortfall, there would generally be no contractual recourse to the Fund’s assets if the Fund holds a non-recourse TOB Residual. However, as described above, a Fund would bear the risk of loss with respect to any Liquidation Shortfall if it holds a recourse TOB Residual.

The SEC and various federal banking and housing agencies recently adopted credit risk retention rules for securitizations (the “Risk Retention Rules”), which take effect in December 2016. The Risk Retention Rules would require the sponsor of a TOB Trust to retain at least 5% of the credit risk of the underlying assets supporting the TOB Trust’s Municipal Bonds. The Risk Retention Rules may adversely affect the Fund’s ability to engage in TOB Trust transactions or increase the costs of such transactions in certain circumstances.

There can be no assurance that a Fund can successfully enter into restructured TOB Trust transactions in order to refinance its existing TOB Residual holdings prior to the compliance date for the Volcker Rule, which may require that the Fund unwinds existing TOB Trusts.

TOB Trust transactions constitute an important component of the municipal bond market. Accordingly, implementation of the Volcker Rule may adversely impact the municipal market, including through reduced demand for and liquidity of municipal bonds and increased financing costs for municipal issuers. Any such developments could adversely affect the Funds. The ultimate impact of these rules on the TOB market and the overall municipal market is not yet certain.

The section entitled “Investment Risks and Considerations—Tax-Exempt Derivatives” in Part II of each Fund’s current Statement of Additional Information is deleted in its entirety and replaced with the following:

Tax-Exempt Derivatives. Certain Funds may hold tax-exempt derivatives which may be in the form of tender option bonds, participations, beneficial interests in a trust, partnership interests or other forms. A number of different structures have been used. For example, interests in long-term fixed-rate municipal debt obligations, held by a trustee or custodian, are coupled with tender option, demand and other features when the tax-exempt derivatives are created. Together, these features entitle the holder of the interest to tender (or put) the underlying municipal debt obligation to a third party at periodic intervals and to receive the principal amount thereof. In some cases, municipal debt obligations are represented by custodial receipts evidencing rights to receive specific future interest payments, principal payments, or both, on the underlying securities held by the custodian. Under such arrangements, the holder of the custodial receipt has the option to tender the underlying securities at their face value to the sponsor (e.g., a Fund, or a bank or broker dealer or other financial institution), which is paid periodic fees equal to the difference between the securities’ fixed coupon rate and the rate that would cause the securities, coupled with the tender option, to trade at par on the date of a rate adjustment. A participation interest gives the Fund an undivided interest in a Municipal Bond in the proportion the Fund’s participation bears to the total principal amount of the Municipal Bond, and typically provides for a repurchase feature for all or any part of the full principal amount of the participation interest, plus accrued interest. Trusts and partnerships are typically used to convert long-term fixed rate high quality bonds of a single state or municipal issuer into variable or floating rate demand instruments. The Municipal Bond Funds may hold tax-exempt derivatives, such as participation interests and custodial receipts, for municipal debt obligations which give the holder the right to receive payment of principal subject to the conditions described above. The Internal Revenue Service (the “IRS”) has not ruled on whether the interest received on tax-exempt derivatives in the form of participation interests or custodial receipts is tax-exempt, and accordingly, purchases of any such interests or receipts are based on the opinions of counsel to the sponsors of such derivative securities. Neither a Fund nor its investment adviser or sub-advisers will review the proceedings related to the creation of any tax-exempt derivatives or the basis for such opinions.

Shareholders should retain this Supplement for future reference.