3. REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Net sales	$ 3,163	$ 7,393	$ 13,814	$ 22,286
Systems
Net sales	404	4,345	5,922	12,851
Contactors
Net sales	1,445	747	3,541	5,291
Services
Net sales	1,314	2,301	4,351	4,144
Wafer-level
Net sales	2,046	2,934	8,240	9,898
Test During Burn-In
Net sales	$ 1,117	$ 4,459	$ 5,574	$ 12,388

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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