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

12 Months Ended

May 31, 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, 2017	$	2,249		$	—	$	2,249
Other comprehensive income (loss) before reclassifications		43			—		43
Amounts reclassified out of AOCI		—			—		—
Other comprehensive income (loss), net of tax		43			—		43
Balance at May 31, 2018	$	2,292		$	—	$	2,292
Other comprehensive income (loss) before reclassifications		(62	)		—		(62	)
Amounts reclassified out of AOCI		—			—		—
Other comprehensive income (loss), net of tax		(62	)		—		(62	)
Balance at May 31, 2019	$	2,230		$	—	$	2,230

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

    The following table summarizes the stock-based compensation expense for the fiscal years ended May 31, 2019, 2018 and 2017 (in thousands, except per share data):

	Year Ended May 31,
	2019		2018		2017
Stock-based compensation in the form of stock options, RSUs, and ESPP purchase rights, included in:
Cost of sales	$	104	$	148	$	91
Selling, general and administrative		545		592		714
Research and development		256		256		194
Net effect on net income (loss)	$	905	$	996	$	999
Effect on net income (loss) per share:
Basic	$	0.04	$	0.05	$	0.06
Diluted	$	0.04	$	0.04	$	0.06

Fair value assumptions for Option Valuation Model

    Fair Value. The fair values of the Company’s stock options granted to employees in fiscal 2019, 2018 and 2017 were estimated using the following weighted average assumptions in the Black-Scholes option valuation method:

	Year Ended May 31,
	2019			2018			2017
Expected term (in years)		5			4			4
Volatility		0.72			0.77			0.81
Risk-free interest rates		2.83	%		1.95	%		1.02	%
Weighted-average grant date fair value	$	1.33		$	2.07		$	1.09

Fair value assumption of the ESPP Purchase Rights

    The fair value of our ESPP purchase rights for the fiscal 2019, 2018 and 2017 was estimated using the following weighted-average assumptions:

	Year End May 31,
	2019			2018			2017
Expected term (in years)		0.5 – 2.0			0.5 – 2.0			0.5 – 2.0
Volatility		0.48 – 0.78			0.56 – 0.81			0.79 – 1.08
Risk-free interest rates		2.33%-2.82	%		1.92%-2.25	%		0.48%-0.80	%
Weighted-average grant date fair value	$	1.14		$	1.01		$	1.65

Stock option and RSU transactions

    The following tables summarize the Company’s stock option and RSU transactions during fiscal 2019, 2018 and 2017 (in thousands):

	Available
	Shares
Balance, May 31, 2016		1,847
Additional shares reserved		2,238
Options granted		(368	)
RSUs granted		(157	)
Options terminated		55
Plan shares expired		(1,446	)
Balance, May 31, 2017		2,169
Options granted		(338	)
RSUs granted		(64	)
RSUs cancelled		33
Options terminated		16
Plan shares expired		(4	)
Balance, May 31, 2018		1,812
Options granted		(804	)
RSUs cancelled		8
Options terminated		195
Plan shares expired		(64	)
Balance, May 31, 2019		1,147

Stock option transactions

    The following table summarized the stock option transactions during fiscal 2019, 2018 and 2017 (in thousands, except per share data):

	Outstanding Options
				Weighted
	Number			Average		Aggregate
	of			Exercise		Intrinsic
	Shares			Price		Value
Balances, May 31, 2016	3,201		$	1.66	$	189
Options granted	368		$	1.83
Options terminated	(55	)	$	1.42
Options exercised	(440	)	$	1.35
Balances, May 31, 2017	3,074		$	1.73	$	8,763
Options granted	338		$	3.56
Options terminated	(16	)	$	2.72
Options exercised	(537	)	$	1.17
Balances, May 31, 2018	2,859		$	2.04	$	1,987
Options granted	804		$	2.19
Options terminated	(195	)	$	2.32
Options exercised	(361	)	$	0.85
Balances, May 31, 2019	3,107		$	2.20	$	283
Options fully vested and expected to vest at May 31, 2019	3,079		$	2.20	$	282

Options outstanding

    The options outstanding and exercisable at May 31, 2019 were in the following exercise price ranges (in thousands, except per share data):

		Options Outstanding						Options Exercisable
		at May 31, 2019						at May 31, 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		0.52	$	0.85		47		0.52	$	0.85
$	1.09-$1.28		456		0.78	$	1.28		456		0.78	$	1.28
$	1.65-$2.06		761		4.57	$	1.83		427		3.50	$	1.79
$	2.10-$2.81		1,600		3.55	$	2.43		1,244		2.81	$	2.44
$	3.46-$3.93		243		5.16	$	3.85		140		5.20	$	3.79
$	0.80-$3.93		3,107		3.47	$	2.20		2,314		2.64	$	2.14	$	274