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Basis of Preparation of Financial Statements and Principal Accounting Policies - Summary of Ownership Interests in Subsidiaries (Detail) | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
ChipMOS U.S.A., Inc [member] |  |
Disclosure of joint ventures [line items] |  |
Name of investor | The Company |
Main businesses | Research, development and marketing of semiconductors, circuits, and electronic related products |
Location | San Jose, USA |
Percentage of Ownership (%) | 100.00% | 100.00%
ChipMOS BVI [member] |  |
Disclosure of joint ventures [line items] |  |
Name of investor | The Company |
Main businesses | Holding company |
Location | British Virgin Islands |
Percentage of Ownership (%) | 100.00% | 100.00%

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- Definition The proportion of ownership interest in a subsidiary attributable to the entity. [Refer: Subsidiaries [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2019-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2019-en-r&anchor=para_17_b_iii&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2019-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2019-en-r&anchor=para_16_b_iii&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2019-01-01 -Paragraph 19B -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_19B_c&doctype=Standard -URIDate 2019-03-27 + Details
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