Upon completion of its IPO in November 2019, the Company adopted the SiTime Corporation 2019 Stock Incentive Plan (the “2019 Plan”), which initially reserved approximately 3.4 million shares of the Company’s common stock. The 2019 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards, and other forms of equity compensation (collectively, “stock awards”), and cash awards, all of which may be granted to employees (including officers), directors, and consultants or affiliates. Awards granted under the 2019 Plan vest at the rate specified by the plan administrator, for restricted stock unit awards primarily over two to five years. As of December 31, 2021, 0.4 million shares were still reserved for issuance.

Activity of RSUs, cash restricted stock unit award (“CRSU”) and performance based restricted stock unit awards ("PRSU") granted under the 2019 Plan is set forth below:


	RSU			Grant Date		CRSU			Grant Date		PRSU		Grant Date
	Number of			Fair Value		Number of			Fair Value		Number of		Fair Value
	Shares			per share		Shares			per share		Shares		per share
Balance at December 31, 2018		—			—		—			—		—		—
Granted		3,012,399			13.00		—			—		—		—
Vested		(23,077	)		13.00		—			—		—		—
Forfeited		-			—		—			—		—		—
Balance at December 31, 2019		2,989,322			13.00		—			—		—		—
Granted		682,517			53.42		11,844			48.62		—		-
Vested		(766,934	)		15.46		(11,220	)		49.37		—		-
Forfeited		(169,199	)		13.72		—			—		—		—
Balance at December 31, 2020		2,735,706			22.35		624			35.05		—		-
Granted		438,474			128.55		3,025			111.93		58,954		261.39
Vested		(874,462	)		27.94		(3,649	)		98.78		—		-
Forfeited		(72,521	)		33.34		—			—		—		—
Balance at December 31, 2021		2,227,197			40.56		—			-		58,954		261.39

The difference between the number of RSUs vested and the shares of common stock issued during the year ended December 31, 2020 is the result of RSUs withheld in satisfaction of minimum tax withholding obligations associated with the vesting. The total fair value, as of the vesting date, of awards vested during the years ended December 31, 2021, 2020 and 2019 were $161.2 million, $43.7 million and $0.3 million, respectively.

On August 4, 2020, the Compensation Committee of the Company adopted and approved the Executive Bonus and Retention Plan (the “Bonus and Retention Plan”). In August 2020, the Compensation Committee approved target bonus amounts and performance goals for the second half of the fiscal year 2020 (the “2020 Goals”), in January 2021, the Compensation Committee approved target bonus amounts and performance goals for the first half of the fiscal year 2021 (the “1H2021 Goals”), and in July 2021 the Compensation Committee approved target bonus amounts and performance goals for the second half of the fiscal year 2021 (the “2H2021 Goals”). The 2020 Goals, the 1H2021 Goals and the 2H2021 Goals are based on the achievement of revenue and Non-GAAP operating profit, as well as individual performance goals. The awards for the actual payouts are granted in the quarter following the end of the performance period. The target bonuses were granted based on a fixed dollar amount to be settled in a variable amount of RSUs on the vesting date and hence the awards have been classified as liability-based awards until settled. Such expense is included in the non-cash adjustment within stock-based compensation expense on the consolidated cash flow statements.

When such awards are granted in RSUs upon achievement of goals, the Company reclassifies the liability to additional paid in capital. The liability of $1.5 million for 2H2021 Goals was recorded as accrued expenses and other current liabilities in the consolidated balance sheet as of December 31, 2021. Actual payouts for 2020 Goals ranged from 119% to 144% of target, for 1H2021 Goals ranged from 76% to 141% of target, and 2H2021 Goals ranged from 138% to 150% of target, in each case based on performance.

On December 17, 2021, the Compensation Committee of the Company approved PRSUs with performance goals for the year 2022 (the “PRSU 2022 Goals”). The PRSU 2022 Goals are based on the achievement of revenue. These grants are included in the RSU awards granted in the table above.

In the year ended December 31, 2020, the Company granted CRSUs as part of an employee bonus plan. The Company ended this program effective April 1, 2021. Generally, such units were granted quarterly and fully vested at the end of the quarter they were granted except units granted to new hires that had a one-year cliff vesting. Such awards were classified as liability-based awards.

Total stock-based compensation expense for employees recognized in the consolidated statements of operations and comprehensive income (loss) was as follows:


	Year Ended December 31,
	2021		2020		2019
	(in thousands)
Equity based awards
Cost of revenue	$	1,654	$	613	$	36
Research and development		11,087		4,682		346
Selling, general and administrative		14,422		9,521		997
	$	27,163	$	14,816	$	1,379
Liability based awards - to be settled in equity
Cost of revenue	$	114	$	—	$	—
Research and development		492		445		-
Selling, general and administrative		2,223		748		-
		2,829		1,193		-
Total stock-based compensation - equity and liability based	$	29,992	$	16,009	$	1,379

Liability based awards - cash settled
Cost of revenue	$	102	$	264	$	—
Research and development		143		415		-
Selling, general and administrative		108		278		-
	$	353	$	957	$	—
Total stock-based compensation expense	$	30,345	$	16,966	$	1,379


Stock-based compensation expense recorded to additional paid-in capital
Equity based awards	$	27,163	$	14,816	$	1,379
Liability based awards - settled in equity		2,531		-		-
Total stock-based compensation expense recorded to additional paid-in capital	$	29,694	$	14,816	$	1,379

At December 31, 2021, there was $82.5 million and $0.6 million of unrecognized compensation costs related to RSUs granted and liability-based awards, respectively. The unrecognized compensation cost is expected to be recognized over a weighted average period of 3.24 years and 0.43 years for liability-based awards.