12. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Tables)

9 Months Ended

Feb. 28, 2019

Equity [Abstract]

Changes in the components of AOCI

    Changes in the components of AOCI, net of tax, were as follows (in thousands):

	Cumulative Translation Adjustments			Unrealized Loss on Investments, Net		Total
Balance at May 31, 2018	$	2,292		$	--	$	2,292
Other comprehensive (loss) income before reclassifications		(40	)		--		(40	)
Amounts reclassified out of AOCI		--			--		--
Other comprehensive (loss) income, net of tax		(40	)		--		(40	)
Balance at February 28, 2019	$	2,252		$	--	$	2,252

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, 2019 and 2018 (in thousands):

	Three Months Ended				Nine Months Ended
	February 28,				February 28,
	2019		2018		2019		2018
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Cost of sales	$	24	$	28	$	83	$	107
Selling, general and administrative		137		162		421		530
Research and development		64		52		201		185
Total stock-based compensation	$	225	$	242	$	705	$	822

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 nine months ended February 28, 2019 and 2018 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,
	2019			2018			2019			2018
Expected term (in years)		5			4			5			4
Volatility		0.69			0.73			0.72			0.77
Risk-free interest rate		2.77	%		2.31	%		2.83	%		1.81	%
Weighted average grant date fair value	$	1.01		$	1.53		$	1.34		$	2.17

    The fair values of the ESPP purchase rights granted for the nine months ended February 28, 2019 were estimated using the following weighted-average assumptions:

	Nine Months Ended
	February 28, 2019
Expected term (in years)		0.5-2.0
Volatility		0.48-0.64
Expected dividend	$	0.00
Risk-free interest rates		2.40%-2.82%
Estimated forfeiture rate		0%
Weighted average grant date fair value	$	1.15

Stock option and RSU transactions

    The following tables summarize the Company’s stock option and RSU transactions during three and nine months ended February 28, 2019 (in thousands):

	Available
	Shares
Balance, May 31, 2018		1,812
Options granted		(441	)
Shares cancelled		13
Shares expired		(11	)
Balance, August 31, 2018		1,373
Options granted		(248	)
Shares cancelled		45
Shares expired		(33	)
Balance, November 30, 2018		1,137
Options granted		(100	)
Shares cancelled		51
Shares expired		(1	)
Balance, February 28, 2019		1,087

Stock option transactions

    The following table summarizes the stock option transactions during the three and nine months ended February 28, 2019 (in thousands, except per share data):

	Outstanding Options
				Weighted
	Number			Average		Aggregate
	of			Exercise		Intrinsic
	Shares			Price		Value
Balances, May 31, 2018		2,859		$	2.04	$	1,987
Options granted		441		$	2.40
Options cancelled		(13	)	$	1.64
Options exercised		(98	)	$	1.12
Balances, August 31, 2018		3,189		$	2.12	$	1,757
Options granted		248		$	2.03
Options cancelled		(45	)	$	2.70
Options exercised		(19	)	$	1.09
Balances, November 30, 2018		3,373		$	2.11	$	679
Options granted		100		$	1.71
Options cancelled		(51	)	$	1.72
Options exercised		(202	)	$	0.61
Balances, February 28, 2019		3,220		$	2.20	$	120
Options fully vested and expected to vest at February 28, 2019		3,184		$	2.20	$	120

Options outstanding

    The options outstanding and exercisable at February 28, 2019 were in the following exercise price ranges (in thousands, except per share data):

		Options Outstanding						Options Exercisable
		at February 28, 2019						at February 28, 2019
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
$	0.80-$0.97		47		0.77	$	0.85		47		0.77	$	0.85
$	1.09-$1.28		498		0.97	$	1.28		498		0.97	$	1.28
$	1.68-$2.06		763		4.76	$	1.83		386		3.54	$	1.79
$	2.10-$2.81		1,651		3.88	$	2.43		1,199		2.98	$	2.44
$	3.46-$3.93		261		5.41	$	3.86		128		5.45	$	3.78
$	0.80-$3.93		3,220		3.72	$	2.20		2,258		2.73	$	2.11	$	120