2. STOCK-BASED COMPENSATION - Compensation costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012	Nov. 30, 2013	Nov. 30, 2012
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 247	$ 99	$ 390	$ 226
Cost of Sales
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	15	7	23	17
Selling, General and Administrative
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	183	66	287	156
Research and Development
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 49	$ 26	$ 80	$ 53