2. STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Aug. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [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, 2017 and 2016 (in thousands):

	Three Months Ended
	August 31,
	2017		2016
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Cost of sales	$	22	$	24
Selling, general and administrative		150		247
Research and development		44		48
Total stock-based compensation	$	216	$	319

Assumptions for options valuation model

    The fair value of the Company’s stock options granted to employees for the three months ended August 31, 2017 and 2016 were estimated using the following weighted average assumptions in the Black-Scholes option valuation model:

	Three Months Ended
	August 31,
	2017			2016
Expected term (in years)		4			4
Volatility		0.78			0.82
Risk-free interest rate		1.75	%		1.01	%
Weighted average grant date fair value	$	2.27		$	1.00

Stock option and RSU transactions

    The following tables summarize the Company’s stock option and RSU transactions during three months ended August 31, 2017 (in thousands):

	Available
	Shares
Balance, May 31, 2017		2,169
Options granted		(224	)
RSUs granted		(64	)
Shares cancelled		--
Balance, August 31, 2017		1,881

Stock option transactions

    The following table summarizes the stock option transactions during the three months ended August 31, 2017 (in thousands, except per share data):

	Outstanding Options
				Weighted
	Number			Average		Aggregate
	of			Exercise		Intrinsic
	Shares			Price		Value
Balances, May 31, 2017		3,074		$	1.73	$	8,763
Options granted		224		$	3.93
Options cancelled		--		$	--
Options exercised		(189	)	$	1.23
Balances, August 31, 2017		3,109		$	1.92	$	4,612
Options fully vested and expected to vest at August 31, 2017		3,072		$	1.92	$	4,577

Options outstanding

    The options outstanding and exercisable at August 31, 2017 were in the following exercise price ranges (in thousands, except per share data):

		Options Outstanding						Options Exercisable
		at August 31, 2017						at August 31, 2017
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
$	0.59-$0.97		454		1.54	$	0.67		454		1.54	$	0.67
$	1.09-$1.36		688		2.32	$	1.27		688		2.32	$	1.27
$	1.68-$2.06		516		4.90	$	1.75		285		4.10	$	1.81
$	2.10-$2.81		1,227		4.27	$	2.44		914		4.24	$	2.46
$	3.93		224		6.86	$	3.99		5		6.86	$	3.99
$	0.59-$3.93		3,109		3.73	$	1.92		2,346		3.14	$	1.69	$3,919