2. REVENUE (Details) - USD ($) $ in Thousands	12 Months Ended
May 31, 2019	May 31, 2018	May 31, 2017
Net sales	$ 21,056	$ 29,555	$ 18,898
Systems
Net sales	9,566	18,174	12,115
Contactors
Net sales	6,154	6,500	1,991
Services
Net sales	5,336	4,881	4,792
Wafer-level
Net sales	14,618	13,080	9,582
Test During Burn-In
Net sales	$ 6,438	$ 16,475	$ 9,316

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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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration