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Summary of Significant Accounting Policies - Summary of Ownership Interests in Subsidiaries (Detail) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
ChipMOS U.S.A., Inc. [member] |  |
Disclosure of joint ventures [line items] |  |
Name of investor | The Company |
Main businesses | Marketing of semiconductors and electronic related products |
Location | San Jose, USA |
Percentage of Ownership (%) | 100.00% | 100.00%
ChipMOS TECHNOLOGIES (BVI) LTD. [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%
ChipMOS SEMICONDUCTORS (Shanghai) LTD. [Member] |  |
Disclosure of joint ventures [line items] |  |
Name of investor | ChipMOS BVI |
Main businesses | Marketing of semiconductors and electronic related products |
Location | Shanghai, People’s Republic of China (“PRC”) |
Percentage of Ownership (%) | 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 2020-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2020-en-r&anchor=para_17_b_iii&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2020-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2020-en-r&anchor=para_16_b_iii&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2020-01-01 -Paragraph 19B -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2020-en-r&anchor=para_19B_c&doctype=Standard -URIDate 2020-01-01 + Details
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