3. REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Net sales	$ 5,267	$ 6,111	$ 8,962	$ 18,518
Systems
Net sales	2,435	2,138	3,407	8,099
Contactors
Net sales	1,930	3,094	3,330	7,790
Services
Net sales	902	879	2,225	2,629
Wafer-level
Net sales	4,993	5,408	7,804	16,570
Test During Burn-In
Net sales	$ 274	$ 703	$ 1,158	$ 1,948