Vicor currently grants options for the purchase of Common Stock (i.e., “stock options”) under the following equity compensation plans that are stockholder-approved:

Amended and Restated 2000 Stock Option and Incentive Plan, as amended and restated (the “2000 Plan”) — Under the 2000 Plan, the Board of Directors or the Compensation Committee of the Board of Directors may grant stock incentive awards based on the Company’s Common Stock, including stock options, stock appreciation rights, restricted stock, performance shares, unrestricted stock, deferred stock, and dividend equivalent rights. Awards may be granted to employees and other key persons, including non-employee directors. Incentive stock options may be granted to employees at a price at least equal to the fair market value per share of the Common Stock on the date of grant, and non-qualified options may be granted to non-employee directors at a price at least equal to 85% of the fair market value of the Common Stock on the date of grant. A total of 10,000,000 shares of Common Stock have been reserved for issuance under the 2000 Plan. The period of time during which an option may be exercised and the vesting periods are determined by the Compensation Committee. The term of each option may not exceed 10 years from the date of grant and have a vesting period of five years.

Vicor Corporation 2017 Employee Stock Purchase Plan (the “Plan” or the “ESPP”). Under the ESPP, the Company has reserved 2,000,000 shares of Common Stock for issuance to eligible employees who elect to participate. The ESPP is intended to qualify as an “employee stock purchase plan” under Section 423 of the Internal Revenue Code. The ESPP operates in successive periods of approximately six months, each referred to as an “offering period.” Generally, offering periods commence on or around September 1 and March 1 and end on or around the following February 28 or August 31, respectively. Under the ESPP, an option is granted to participating employees on the first day of an offering period to purchase shares of the Company’s Common Stock at the end of that offering period at a purchase price equal to 85% of the lesser of the fair market value of a share of Common Stock on either the first day or the last day of that offering period. The purchase of shares is funded by means of periodic payroll deductions, which may not exceed 15.0% of the employee’s eligible compensation, as defined in the Plan. Among other provisions, the Plan limits the number of shares that can be purchased by a participant during any offering period and cumulatively for any calendar year.

Stock-based compensation expense for the years ended December 31 was as follows (in thousands):


	2023		2022		2021
Cost of revenues	$	2,429	$	1,648	$	1,000
Selling, general and administrative		6,829		5,735		3,873
Research and development		3,611		2,881		2,162
Total stock-based compensation	$	12,869	$	10,264	$	7,035

Compensation expense by type of award for the years ended December 31 was as follows (in thousands):


	2023		2022		2021
Stock options	$	11,585	$	9,093	$	6,122
ESPP		1,284		1,171		913
Total stock-based compensation	$	12,869	$	10,264	$	7,035

All time-based (i.e., non-performance-based) options for the purchase of Vicor common stock are granted with an exercise price equal to or greater than the market price for Vicor Common Stock at the date of the grant. The fair value for non-performance-based stock options awarded under the 2000 Plan for the years shown below was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:


	2023			2022			2021
Risk-free interest rate		3.7	%		2.8	%		0.8	%
Expected dividend yield		—			—			—
Expected volatility		54	%		51	%		49	%
Expected term (years)		4.2			4.4			4.9

The Company uses the yield on zero-coupon U.S. Treasury “Strip” securities for a period that is commensurate with the expected term assumption for each vesting period.

The Company determines the expected dividend yield by annualizing the most recent prior cash dividends declared by the Company’s Board of Directors, if any, and dividing that result by the closing stock price on the date of that dividend declaration. Dividends are not paid on options.

Vicor uses historical volatility to estimate the grant-date fair value of the options, using the expected term for the period over which to calculate the volatility (see below). The Company does not expect its future volatility to differ from its historical volatility. The computation of the Company’s volatility is based on a simple average calculation of monthly volatilities over the expected term.

The Company uses historical employee exercise and option expiration data to estimate the expected term assumption for the Black-Scholes grant-date valuation. The Company believes this historical data is currently the best estimate of the expected term of options, and all groups of the Company’s employees exhibit similar exercise behavior.

The amount of stock-based compensation recognized during a period is based on the value of the portion of the awards

that are ultimately expected to vest. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The term “forfeitures” is distinct from “cancellations” or “expirations” and represents only the unvested portion of the surrendered option. The forfeiture analysis is re-evaluated annually and the forfeiture rate is adjusted as necessary. Ultimately, the actual expense recognized over the vesting period will only be for those shares that vest.

Based on an analysis of historical forfeitures, the Company applied an annual forfeiture rate of 5.00% in 2023, estimating approximately 86% of its options would actually vest. For 2022 and 2021, the Company applied an annual forfeiture rate of 5.35% and 4.85%, respectively, estimating approximately 85% and 86%, respectively, of its options would actually vest.

A summary of the activity under the 2000 Plan as of December 31, 2023 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data):


	Options Outstanding			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life in Years		Aggregate Intrinsic Value

Outstanding on December 31, 2022		2,024,664		$	41.48
Granted		918,161		$	42.76
Forfeited and expired		(79,500	)	$	53.67
Exercised		(308,083	)	$	25.31
Outstanding on December 31, 2023		2,555,242		$	43.51		3.90	$	27,948
Exercisable on December 31, 2023		973,894		$	27.39		2.10	$	24,781
Vested or expected to vest as of December 31, 2023(1)		2,404,726		$	43.04		3.79	$	27,619

(1)

In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. The number of options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options.

As of December 31, 2022 and 2021, the Company had options exercisable for 1,046,092 and 776,559 shares, respectively, for which the weighted average exercise prices were $18.26 and $11.63, respectively.

During the years ended December 31, 2023, 2022, and 2021, the total intrinsic value of Vicor options exercised (i.e., the difference between the market price at exercise and the price paid by the employee to exercise the options) was approximately $14,396,000, $7,252,000, and $56,933,000, respectively. The total amount of cash received by the Company from options exercised in 2023, 2022, and 2021 was $7,798,000, $1,634,000, and $7,616,000, respectively. The total grant-date fair value of stock options granted during the years ended December 31, 2023, 2022, and 2021 was approximately $17,957,000, $15,087,000, and $10,506,000, respectively.

As of December 31, 2023, there was approximately $23,179,000 of total unrecognized compensation cost related to unvested awards for Vicor. That cost is expected to be recognized over a weighted-average period of 2.1 years for those awards. The expense will be recognized as follows: $11,028,000 in 2024, $6,730,000 in 2025, $3,638,000 in 2026, $1,473,000 in 2027, and $310,000 in 2028.

The weighted-average fair value of Vicor options granted was $19.56, $26.53, and $39.27, in 2023, 2022, and 2021, respectively.

The Company sponsors a savings plan available to all domestic employees, which qualifies under Section 401(k) of the Code. Employees may contribute to the plan in amounts representing from 1% to 80% of their pre-tax salary, subject to

statutory limitations. The Company matches employee contributions to the plan at a rate of 50%, up to the first 6% of an employee’s compensation. The Company’s matching contributions currently vest at a rate of 20% per year, based upon years of service. The Company’s contributions to the plan were approximately $2,317,000, $2,211,000, and $1,593,000 in 2023, 2022, and 2021, respectively.

Under the Company’s 1985 Stock Bonus Plan, as amended, shares of Common Stock may be awarded to employees from time to time as determined by the Board of Directors. On December 31, 2023, 109,964 shares were available for further award. All shares awarded to employees under this plan have vested. No further awards are contemplated under this plan at the present time.