2. STOCK-BASED COMPENSATION (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	$ 242	$ 257	$ 822	$ 791
Cost of Sales
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	28	22	107	69
Selling, General and Administrative
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	162	187	530	575
Research and Development
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	$ 52	$ 48	$ 185	$ 147