The Equity Compensation Plan provides for the granting of incentive and nonqualified stock options, shares of common stock, stock appreciation rights and performance units to employees, directors and consultants of the Company. Stock options are exercisable over periods determined by the Compensation Committee, but for no longer than 10 years from the grant date. Through December 31, 2020, the Company’s shareholders have approved increases in the number of shares reserved for issuance under the Equity Compensation Plan to 10,500,000, and have extended the term of the plan through 2024. As of December 31, 2020, there were 2,001,339 shares that remained available to be granted under the Equity Compensation Plan.

The Company has issued restricted stock awards and units to employees and non-employees with vesting terms of one to six years. The fair value is equal to the market price of the Company’s common stock on the date of grant for awards granted to employees and equal to the market price at the end of the reporting period for unvested non-employee awards or upon the date of vesting for vested non-employee awards. Expense for restricted stock awards and units is amortized ratably over the vesting period for the awards issued to employees and using a graded vesting method for the awards issued to non-employees.

The following table summarizes the activity related to restricted stock unit (RSU) share based payment awards:

	Number of Shares			Weighted- Average Grant-Date Fair Value
Unvested, January 1, 2020		98,810		$	144.53
Granted		143,179			162.32
Vested		(47,750	)		136.59
Forfeited		(1,615	)		122.83
Unvested, December 31, 2020		192,624		$	160.99

The weighted average grant-date fair value of RSU awards granted was $162.32, $168.95 and $115.48 during the years ended December 31, 2020, 2019 and 2018, respectively. The fair value as of the respective vesting dates of RSUs was $7.7 million, $7.7 million and $8.1 million for 2020, 2019 and 2018, respectively.

The following table summarizes the activity related to restricted stock award (RSA) share based payment awards:

	Number of Shares			Weighted- Average Grant-Date Fair Value
Unvested, January 1, 2020		311,643		$	80.94
Granted		1,926			155.85
Vested		(171,908	)		50.65
Unvested, December 31, 2020		141,661		$	124.81

The weighted average grant-date fair value of RSA awards granted was $155.85, $194.19 and $122.15 during the years ended December 31, 2020, 2019 and 2018, respectively. The fair value as of the respective vesting dates of RSAs was $24.5 million, $28.4 million and $17.7 million for 2020, 2019 and 2018, respectively.

For the years ended December 31, 2020, 2019 and 2018, the Company recorded, as compensation charges related to restricted stock awards and units issued to employees and non-employees, selling, general and administrative expense of $13.9 million, $10.0 million and $7.6 million, respectively, cost of sales of $1.9 million, $1.1 million and $758,000, respectively, and research and development expense of $4.3 million, $2.5 million and $2.0 million, respectively.

In connection with the vesting of restricted stock awards and units during the years ended December 31, 2020, 2019 and 2018, 86,442, 86,075 and 86,679 shares, respectively, with aggregate fair values of $12.5 million, $14.0 million and $9.2 million, respectively, were withheld in satisfaction of tax withholding obligations and are reflected as a financing activity within the Consolidated Statements of Cash Flows.

For the years ended December 31, 2020, 2019 and 2018, the Company recorded as compensation charges related to all restricted stock units to non-employee members of the Scientific Advisory Board, whose unvested shares are marked to market each reporting period, research and development expense of $380,000, $632,000 and $64,000, respectively.

The Company has granted restricted stock units to non-employee members of the Board of Directors with quarterly vesting over a period of approximately one year. The fair value is equal to the market price of the Company’s common stock on the date of grant. The restricted stock units are issued and expense is recognized ratably over the vesting period. For the years ended December 31, 2020, 2019 and 2018, the Company recorded compensation charges for services performed, related to all restricted stock units granted to non-employee members of the Board of Directors, selling, general and administrative expense of $1.3 million, $916,000 and $4.3 million, respectively. In connection with the vesting of the restricted stock, the Company issued to non-employee members of the Board of Directors 6,456, 9,332 and 25,000 shares during the years ended December 31, 2020, 2019 and 2018, respectively.

As of December 31, 2020, the total unrecognized expense related to all restricted stock awards and units was $31.7 million, which the Company expects to recognize over a weighted average period of 1.89 years.

Each performance unit award is subject to both a performance-vesting requirement (either performance-based or market-based) and a service-vesting requirement. The performance-based vesting requirement is tied to the Company's cumulative revenue growth compared to the cumulative revenue growth of companies comprising the Nasdaq Electronics Components Index, as measured over a

specific performance period. The market-based vesting requirement is tied to the Company's total shareholder return relative to the total shareholder return of companies comprising the Nasdaq Electronics Components Index, as measured over a specific performance period. The maximum number of performance units that may vest based on performance is two times the shares granted. Further, if the Company's total shareholder return is negative, the performance units will not vest at all.

The following table summarizes the activity related to performance unit awards (PSU) share based payment awards:

	Number of Shares			Weighted- Average Grant-Date Fair Value
Unvested, January 1, 2020		37,781		$	134.97
Granted		111,410			167.74
Vested		(31,276	)		105.65
Unvested, December 31, 2020		117,915		$	165.48

During the years ended December 31, 2020, 2019 and 2018, the Company granted 95,772, 10,096 and 40,601 performance units, respectively, of which 47,885, 5,050 and 6,022 units, respectively, are subject to performance-based vesting requirements and 47,887, 5,046 and 6,025 units, respectively, are subject to market-based vesting requirements, and will vest over the terms as described above. During the years ended December 31, 2020, 2019 and 2018, there were also 15,638, 15,650 and 28,554 incremental performance-based shares, respectively, that vested resulting from an increased vesting factor based on Company performance. The weighted average grant date fair value of the performance unit awards granted was $167.74, $198.72 and $119.62 during the years ended December 31, 2020, 2019 and 2018, respectively, as determined by the Company’s common stock on date of grant for the units with performance-based vesting and a Monte-Carlo simulation for the units with market-based vesting.

For the years ended December 31, 2020, 2019 and 2018, the Company recorded, as compensation charges related to all performance stock units, selling, general and administrative expense of $4.3 million, $1.7 million and $1.3 million, respectively, cost of sales of $670,000, $208,000 and $141,000, respectively, and research and development expense of $1.1 million, $419,000 and $330,000, respectively.

In connection with the vesting of performance units during the years ended December 31, 2020, 2019 and 2018, 12,877, 16,668 and 25,208 shares, respectively, with aggregate fair values of $1.9 million, $2.6 million and $2.9 million, respectively, were withheld in satisfaction of tax withholding obligations and are reflected as a financing activity within the Consolidated Statements of Cash Flows.

As of December 31, 2020, the total unrecognized compensation expense related to performance unit awards was $12.9 million, which the Company expects to recognize over a weighted average period of 2.12 years.

On April 7, 2009, the Board of Directors of the Company adopted an Employee Stock Purchase Plan (ESPP). The ESPP was approved by the Company’s shareholders and became effective on June 25, 2009. The Company has reserved 1,000,000 shares of common stock for issuance under the ESPP. Unless terminated by the Board of Directors, the ESPP will expire when all reserved shares have been issued.

Eligible employees may elect to contribute to the ESPP through payroll deductions during consecutive three-month purchase periods, the first of which began on July 1, 2009. Each employee who elects to participate will be deemed to have been granted an option to purchase shares of the Company’s common stock on the first day of the purchase period. Unless the employee opts out during the purchase period, the option will automatically be exercised on the last day of the period, which is the purchase date, based on the employee’s accumulated contributions to the ESPP. The purchase price will equal 85% of the lesser of the closing price per share of common stock on the first day of the period or the last business day of the period.

Employees may allocate up to 10% of their base compensation to purchase shares of common stock under the ESPP; however, each employee may purchase no more than 12,500 shares on a given purchase date, and no employee may purchase more than $25,000 of common stock under the ESPP during a given calendar year.

For the years ended December 31, 2020, 2019 and 2018, the Company issued 9,668, 7,492 and 10,303 shares, respectively, of its common stock under the ESPP, resulting in proceeds of $1.2 million, $889,000 and $798,000, respectively. For the years ended December 31, 2020, 2019 and 2018, the Company recorded charges of $96,000, $79,000 and $82,000, respectively, to selling, general and administrative expense, $111,000, $73,000, $81,000, respectively, to cost of sales and $139,000, $118,000 and $130,000,

respectively, to research and development expense, related to the ESPP equal to the amount of the discount and the value of the look-back feature.