STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Aug. 31, 2021

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 months ended August 31, 2021 and 2020 (in thousands):

	Three Months Ended August 31,
	2021		2020
Stock-based compensation in the form of stock options, RSUs and ESPP purchase rights, included in:
Cost of sales	$	82	$	16
Selling, general and administrative		395		205
Research and development		111		49
Total stock-based compensation	$	588	$	270

Fair value assumptions for Option Valuation Model

Fair Value. The fair value of the Company’s stock options granted to employees for the three months ended August 31, 2021 and 2020 were estimated using the following weighted average assumptions in the Black-Scholes option valuation model:

	Three Months Ended August 31,
	2021			2020
Expected term (in years)		6			6
Volatility		0.76			0.71
Risk-free interest rate		1.01	%		0.38	%
Weighted average grant date fair value	$	1.93		$	1.16

Fair value assumption of the ESPP Purchase Rights

Stock option and RSU transactions

The following tables summarize the Company’s stock option and RSU transactions during the three months ended August 31, 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

Stock option transactions

The following table summarizes the stock option transactions during the three months ended August 31, 2021 (in thousands, except per share data):

	Outstanding Options
	Number of Shares			Weighted Average Exercise Price		Aggregate 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 fully vested and expected to vest at August 31, 2021		2,290		$	2.14	$	12,177

Options outstanding

The options outstanding and exercisable at August 31, 2021 were in the following exercise price ranges (in thousands, except per share data):

	Options Outstanding at August 31, 2021						Options Exercisable at August 31, 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		125		5.78	$	1.27		67		5.90	$	1.29
$1.64-$1.86		924		4.60	$	1.70		556		4.20	$	1.69
$2.03-$2.42		883		3.01	$	2.21		702		2.66	$	2.20
$2.76-$2.93		231		6.38	$	2.92		29		3.03	$	2.82
$3.46-$3.93		162		2.90	$	3.87		162		2.90	$	3.87
$1.22-$3.93		2,325		4.12	$	2.14		1,516		3.40	$	2.16	$	8,034