14. STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Aug. 31, 2020

Share-based Payment Arrangement [Abstract]

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, 2020 and 2019 (in thousands):

	Three Months Ended
	August 31,
	2020		2019
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Cost of sales	$	16	$	19
Selling, general and administrative		205		130
Research and development		49		50
Net effect on net income (loss)	$	270	$	199

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, 2020 and 2019 were estimated using the following weighted average assumptions in the Black-Scholes option valuation model:

	Three Months Ended
	August 31,
	2020		2019
Expected term (in years)		6		5
Volatility		0.71		0.71
Risk-free interest rate		0.38%		1.88%
Weighted average grant date fair value	$	1.16	$	0.97

Stock option and RSU transactions

    The following tables summarize the Company’s stock option and RSU transactions during the three months ended August 31, 2020 (in thousands):

	Available
	Shares
Balance, May 31, 2020		1,650
Options granted		(200	)
RSUs granted		(196	)
Options cancelled		188
RSUs cancelled		2
Options expired		(125	)
Balance, August 31, 2020		1,319

Stock option transactions

    The following table summarizes the stock option transactions during the three months ended August 31, 2020 (in thousands, except per share data):

	Outstanding Options
				Weighted
	Number			Average		Aggregate
	of			Exercise		Intrinsic
	Shares			Price		Value
Balances, May 31, 2020	3,153		$	2.17	$	102
Options granted	200		$	1.86
Options cancelled	(188	)	$	2.18
Options exercised	(148	)	$	1.30
Balances, August 31, 2020	3,017		$	2.19	$	148
Options fully vested and expected to vest at August 31, 2020	2,981		$	2.19	$	145

Options outstanding

    The options outstanding and exercisable at August 31, 2020 were in the following exercise price ranges (in thousands, except per share data):

	Options Outstanding						Options Exercisable
	at August 31, 2020						at August 31, 2020
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		75		6.54	$	1.22		8		6.54	$	1.22
$1.64-$1.86		1,105		5.47	$	1.70		546		4.72	$	1.68
$2.03-$2.46		1,162		3.49	$	2.21		846		2.92	$	2.19
$2.63-$2.81		464		1.04	$	2.70		462		1.03	$	2.70
$3.46-$3.93		211		3.90	$	3.86		171		3.91	$	3.85
$1.22-$3.93		3,017		3.94	$	2.19		2,033		3.07	$	2.31	$	59