STOCKBASED COMPENSATION (Tables)

6 Months Ended

Nov. 30, 2021

EQUITY

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

The following table summarizes the stock-based compensation expense for the three and six months ended November 30, 2021 and 2020 (in thousands):

	Three Months Ended November 30,				Six Months Ended November 30,
	2021		2020		2021		2020
Stock-based compensation in the form of stock options, RSUs and ESPP purchase rights, included in:
Cost of sales	$	76	$	15	$	158	$	31
Selling, general and administrative		377		194		772		399
Research and development		265		48		376		97
Total stock-based compensation	$	718	$	257	$	1,306	$	527

Fair value assumptions for Option Valuation Model

Fair Value. The fair value of the Company’s stock options granted to employees for the three and six months ended November 30, 2021 and 2020 were estimated using the following weighted average assumptions in the Black-Scholes option valuation model:

	Three Months Ended November 30,						Six Months Ended November 30,
	2021			2020			2021			2020
Expected term (in years)		6			6			6			6
Volatility		0.85			0.73			0.76			0.72
Risk-free interest rate		1.32	%		0.43	%		1.02	%		0.39	%
Weighted average grant date fair value	$	14.16		$	0.91		$	2.50		$	1.09

Fair value assumption of the ESPP Purchase Rights

 The fair values of the ESPP purchase rights granted for the three and six months ended November 30, 2021 and 2020 were estimated using the following assumptions:

	Three and Six Months Ended			Three and Six Months Ended
	November 30, 2021			November 30, 2020
Expected term (in years)	0.5-2.0			0.5-2.0
Volatility	1.01-1.43			0.74-0.82
Expected dividend	$	0.00		$	0.00
Risk-free interest rates	0.05%-0.27		%	0.10%-0.14		%
Estimated forfeiture rate		0	%		0	%
Weighted average grant date fair value	$	9.57		$	0.42

Stock option and RSU transactions

The following tables summarize the Company’s stock option and RSU transactions during the three and six months ended November 30, 2021 (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 grants		(270	)
Options cancelled		51
Balance, November 30, 2021		1,856

Stock option transactions

The following table summarizes the stock option transactions during the three and six months ended November 30, 2021 (in thousands, except per share data):

	Outstanding Options
	Number of			Weighted Average		Aggregate
	Shares			Exercise Price		Intrinsic 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 fully vested and expected to vest at November 30, 2021		1,685		$	4.22	$	25,250

Options outstanding

 The options outstanding and exercisable at November 30, 2021 were in the following exercise price ranges (in thousands, except per share data):

		Options Outstanding at November 30, 2021						Options Exercisable at November 30, 2021
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		97		5.60	$	1.28		54		5.86	$	1.33
$	1.64-$1.86		682		4.51	$	1.71		356		4.05	$	1.69
$	2.03-$2.46		594		3.18	$	2.23		453		2.87	$	2.22
$	2.63-$2.93		226		6.12	$	2.92		38		3.67	$	2.84
$	3.46-$3.93		104		2.67	$	3.84		104		2.67	$	3.84
$	9.94-19.85		10		6.89	$	19.85		-		6.89	$	19.85
$	1.22-19.85		1,713		4.23	$	2.26		1,005		3.46	$	2.18	$	15,314