The Company has outstanding stock options assumed from acquisitions. A summary of the status of, and changes in, the Company's stock option awards follows (dollars in thousands, except weighted-average exercise price):

Under the terms of the 2020 Equity Plan, the Company has granted RSU, PSU, and DSU awards. The Company grants RSUs to members of management periodically throughout the year. Each RSU is equivalent to one share of the Company’s common stock. These units have requisite service periods ranging from one to five years, subject to accelerated vesting upon eligible retirement from the Company. Recipients earn quarterly dividend equivalents on their respective units which entitle the recipients to additional units. Therefore, dividends earned each quarter compound based upon the updated unit balances.

The Company also grants PSU awards to members of management periodically throughout the year. Each PSU is equivalent to one share of the Company’s common stock. The number of units that ultimately vest will be determined based on the achievement of market or other performance goals, subject to accelerated service-based vesting conditions upon eligible retirement from the Company.

The Company grants DSUs, which are restricted stock units with a deferred settlement date, to its directors and advisory directors. Each DSU is equivalent to one share of the Company’s common stock. DSUs vest over a one-year period following the grant date. These units generally are subject to the same terms as RSUs under the 2020 Equity Plan, except that, following vesting, settlement occurs within 30 days following the earlier of separation from the board or a change in control of the Company. After vesting and prior to delivery, these units will continue to earn dividend equivalents.

Upon exercise or vesting/delivery, shares are expected (though not required) to be issued from treasury.

Restricted Stock Unit, Performance-Based Restricted Stock Unit, and Deferred Stock Unit Awards

(1)

Shares for PSU awards represent target shares at grant date.

On March 24, 2021, under the terms of the 2020 Equity Plan, the Company granted 212,426 RSUs to members of management. The grant date fair value of the award totaled $5.2 million and will be recognized as compensation expense over the requisite service period ranging from one year to five years. The terms of these awards included an accelerated vesting provision upon eligible retirement from the Company, after a one-year minimum requisite service period. Subsequent to the requisite service period, the awards will become 100% vested. Further, the Company granted 33,288 DSUs to directors and advisory directors. The grant date fair value of the award totaled $0.8 million and will be recognized as compensation expense over the requisite service period of one year. Subsequent to the requisite service period, the awards will become 100% vested.

During the first quarter of 2021, the Company also granted a target of 70,815 market-based PSUs with a maximum award of 113,304 units. The actual number of units issued at the vesting date could range from 0% to 160% of the initial grant, depending on attaining the market-based total shareholder return performance goal. The grant date fair value of the award was $1.7 million and will be recognized in compensation expense over the performance period ending December 31, 2023.

Further, during the first quarter of 2021, the Company granted a target of 28,344 PSUs with a maximum award of 39,682 units. The actual number of units issued at the vesting date could range from 0% to 140% of the initial grant, depending on attaining a performance goal based upon FirsTech’s compounded annual revenue growth rate. The grant date fair value of the award is $0.7 million and will be recognized in compensation expense over the performance period ending August 31, 2023, subject to achievement of the performance goal.

On May 19, 2021, under the terms of the 2020 Equity Plan, the Company granted 2,376 DSUs to directors. The grant date fair value of the award totaled $0.1 million and will be recognized as compensation expense over the requisite service period of one year. Subsequent to the requisite service period, the awards will become 100% vested.

On September 22, 2021, under the terms of the 2020 Equity Plan, the Company granted 47,805 RSUs to members of management. The grant date fair value of the award totaled $1.1 million and will be recognized as compensation expense over the requisite service period ranging from three year to five years. Subsequent to the requisite service period, the awards will become 100% vested.

A description of RSU, PSU and DSU awards granted in 2020 and 2019 under the terms of the 2020 Equity Plan, 2010 Equity Plan, or the First Community 2016 Equity Incentive Plan can be found in the Company’s Annual Reports for the years ended December 31, 2020, and 2019.

The Company issued 116,904 treasury shares in conjunction with the vesting of RSUs and settlement of DSUs in 2021. The difference between the number of shares issued and the number of vested units is due to shares issued under a net share settlement option.

2021 Employee Stock Purchase Plan

The 2021 ESPP was approved at the Company’s 2021 Annual Meeting of Stockholders, replacing the 2011 ESPP which terminated at the end of 2020. The purpose of the 2021 ESPP is to provide a means through which our employees may acquire a proprietary interest in the Company by purchasing shares of our common stock at a 15% discount through voluntary payroll deductions, to assist us in retaining the services of our employees and securing and retaining the services of new employees, and to provide incentives for our employees to exert maximum efforts toward our success. Under the terms of the 2021 ESPP, all participating employees will have equal rights and privileges. Substantially all of our employees are eligible to participate in the 2021 ESPP. Further details can be found within First Busey’s Definitive Proxy Statement filed with the SEC on April 8, 2021.

The first offering under the 2021 ESPP began on July 1, 2021. There were 569,610 shares available for issuance under the 2021 ESPP as of December 31, 2021.

Stock-based Compensation Expense

The Company recognized compensation expense related to non-vested RSU, PSU, and DSU awards, as well as the 2021 ESPP, as presented in the table below (dollars in thousands):


	Years Ended December 31,
	2021		2020		2019
Stock-based compensation expense
Stock options ⁽¹⁾	$	—	$	—	$	146
RSU awards		5,809		6,493		3,249
PSU awards		979		77		—
DSU awards		962		565		602
2021 ESPP		114		—		—
Total stock-based compensation expense	$	7,864	$	7,135	$	3,997

(1)

Stock option compensation expense recorded in 2019 was attributable to converted options related to the 2017 acquisition of First Community.

Unamortized stock-based compensation expense is presented in the table below (dollars in thousands):


	As of December 31,
	2021			2020
Unamortized stock-based compensation
RSU awards	$	10,204		$	10,411
PSU awards		1,547			179
DSU awards		209			294
Total unamortized stock-based compensation	$	11,960		$	10,884

Weighted average period over which expense is to be recognized		2.9	yrs		3.0	yrs