2. STOCK-BASED COMPENSATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2017	Nov. 30, 2016	Nov. 30, 2017	Nov. 30, 2016
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	$ 364	$ 215	$ 580	$ 534
Cost of Sales
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	57	23	79	47
Selling, General and Administrative
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	218	141	368	388
Research and Development
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	$ 89	$ 51	$ 133	$ 99