STOCK-BASED COMPENSATION (Tables)

9 Months Ended

Feb. 28, 2022

STOCK-BASED COMPENSATION

Compensation costs related to the Company's stock-based compensation

The following table summarizes the stock-based compensation expense for the three and nine months ended February 28, 2022 and 2021 (in thousands):

	Three Months Ended				Nine Months Ended
	February 28,				February 28,
	2022		2021		2022		2021
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Cost of sales	$	90	$	14	$	248	$	45
Selling, general and administrative		487		194		1,259		593
Research and development		303		63		679		160
Total stock-based compensation	$	880	$	271	$	2,186	$	798

Fair value assumptions for Option Valuation Model

Fair Value. The fair values of the Company’s stock options granted to employees for the three and nine months ended February 28, 2022 and 2021, were estimated using the following weighted average assumptions in the Black-Scholes option valuation model:

	Three Months Ended			Nine Months Ended
	February 28,			February 28,
	2022			2022			2021
Expected term (in years)		5			6			6
Volatility		117	%		77	%		72	%
Risk-free interest rate		1.56	%		1.03	%		0.39	%
Weighted average grant date fair value	$	9.43		$	2.56		$	1.09

Fair value assumption of the ESPP Purchase Rights

The fair values of the ESPP purchase rights granted for the nine months ended February 28, 2022 and 2021 were estimated using the following assumptions:

	Nine Months Ended		Nine Months Ended
	February 28, 2022		February 28, 2021
Expected term (in years)	0.5-2.0		0.5-2.0
Volatility	101%-143%		74%-82%
Risk-free interest rates	0.05%-0.27%		0.10%-0.14%
Weighted average grant date fair value	$	9.57	$	0.44

Stock option and RSU transactions

The following tables summarize the Company’s stock option and RSU transactions during the three and nine months ended February 28, 2022 and shows the shares available to be issued at the end of each period (in thousands):

	Available
	Shares
Balance, May 31, 2021		1,137
Options granted		(206	)
RSUs granted		(238	)
Options cancelled and adjusted		(8	)
Balance, August 31, 2021		685
Options reserved		1,414
Options granted		(10	)
RSUs granted		(14	)
RSUs performance-based grants		(270	)
Options cancelled		51
Balance, November 30, 2021		1,856
Options granted		(2	)
RSUs cancelled		10
Options cancelled		41
Balance, February 28, 2022		1,905

Stock option transactions

The following table summarizes the stock option transactions during the three and nine months ended February 28, 2022 (in thousands, except per share data):

	Outstanding Options
				Weighted
	Number			Average		Aggregate
	of			Exercise		Intrinsic
	Shares			Price		Value
Balances, May 31, 2021		2,766		$	2.16	$	807
Options granted		206		$	2.93
Options cancelled		(6	)	$	1.95
Options exercised		(641	)	$	2.46
Balances, August 31, 2021		2,325		$	2.14	$	12,365
Options granted		10		$	19.85
Options cancelled		(51	)	$	1.73
Options exercised		(571	)	$	2.14
Balances, November 30, 2021		1,713		$	2.26	$	25,997
Options granted		2		$	11.55
Options cancelled		(41	)	$	1.22
Options exercised		(66	)	$	2.03
Balances, February 28, 2022		1,608		$	2.29	$	18,248
Options fully vested and expected to vest at February 28, 2022		1,582		$	2.30	$	17,952

Options outstanding

The options outstanding and exercisable at February 28, 2022 were in the following exercise price ranges (in thousands, except per share data):

	Options Outstanding at February 28, 2022						Options Exercisable at February 28, 2022
Range of Exercise Prices	Number Outstanding Shares		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable Shares		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Aggregate Intrinsic Value
$1.22-$1.34		51		5.64	$	1.34		51		5.64	$	1.34
$1.64-$1.86		671		4.27	$	1.71		387		3.89	$	1.69
$2.03-$2.46		547		3.13	$	2.23		447		2.92	$	2.23
$2.63-$2.93		223		5.87	$	2.92		47		4.01	$	2.86
$3.46-$3.93		104		2.42	$	3.84		104		2.42	$	3.84
$9.94-$19.85		12		6.69	$	16.54		1		6.65	$	19.46
$1.22-$19.85		1,608		4.04	$	2.29		1,037		3.42	$	2.19	$	11,831