3. REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Net sales	$ 6,874	$ 5,911	$ 12,407	$ 10,651
Systems
Net sales	3,027	3,712	5,961	5,518
Contactors
Net sales	3,046	943	4,696	2,096
Services
Net sales	801	1,256	1,750	3,037
Wafer-level
Net sales	6,335	4,226	11,161	6,195
Test During Burn-In
Net sales	$ 539	$ 1,685	$ 1,246	$ 4,456

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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