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v3.20.1

Investments Accounted for Using the Equity Method - Additional Information (Detail) ¥ in Thousands, shares in Thousands, $ in Thousands, $ in Thousands, $ in Thousands | 1 Months Ended | 12 Months Ended |  |
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Jul. 31, 2019 TWD ($) | Jul. 31, 2019 USD ($) | Jul. 31, 2019 SGD ($) | May 31, 2019 TWD ($) | May 31, 2019 USD ($) | Apr. 30, 2019 TWD ($) shares | Apr. 30, 2019 USD ($) shares | Mar. 31, 2019 CNY (¥) | Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2019 CNY (¥) | Mar. 31, 2019 TWD ($) | Mar. 31, 2019 USD ($)
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain recognized from remeasuring fair value of equity interest before business combination |  |  |  |  |  | $ 243,057 | $ 8,126 |  |  |  |  |  |  |  |  |
Capital surplus |  |  |  |  |  |  |  |  | $ 138,910,363 |  | $ 143,276,664 |  | $ 4,644,279 |  |  |
Impairment losses on financial assets |  |  |  |  |  |  |  |  | 400,201 | $ 13,380 | 521,010 | $ 50,206 |  |  |  |
Investments in joint ventures |  |  |  |  |  |  |  |  | $ 279,702 |  | $ 180,494 |  | 9,351 |  |  |
ASE Test, Inc. [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in associate |  |  |  |  |  | 50.97% | 50.97% |  |  |  |  |  |  |  |  |
Percentage of ownership |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00% |  |  |  |  |
ASE Test, Inc. [member] | Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid in cash for shares |  |  |  |  |  | $ 250,000 | $ 8,358 |  |  |  |  |  |  |  |  |
Shares subscribed | shares |  |  |  |  |  | 100,000 | 100,000 |  |  |  |  |  |  |  |  |
Universal Global Technology Co., Limited [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid in cash for shares | $ 1,824,608 | $ 61,003 | $ 79,863 |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership | 42.23% | 42.23% | 42.23% |  |  |  |  |  | 75.30% | 75.30% | 74.60% |  |  |  |  |
ChipMos Technologies Inc [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in associate |  |  |  |  |  |  |  |  | 20.48% | 20.48% | 20.47% |  |  |  |  |
Capital surplus |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,016 | $ 67
Deca Technologies Inc. [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in associate |  |  |  |  |  |  |  |  | 22.02% | 22.02% | 22.04% |  |  |  |  |
ASE Embedded Electronics Inc. [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain recognized from remeasuring fair value of equity interest before business combination |  |  |  |  |  | $ 76,655 | $ 2,563 |  |  |  |  |  |  |  |  |
Ordinary shares acquired |  |  |  | $ 150,000 | $ 150,000 |  |  |  |  |  |  |  |  |  |  |
Consideration paid in cash for shares |  |  |  | $ 1,500,000 | $ 50,150 |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in joint venture |  |  |  |  |  |  |  |  |  |  | 51.00% |  |  |  |  |
Percentage of ownership | 100.00% | 100.00% | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Investments in joint ventures |  |  |  |  |  |  |  |  |  |  | $ 180,494 |  |  |  |  |
Accumulated deficits compensated by capital reduction |  |  |  |  |  | $ 1,147,595 | $ 38,368 |  |  |  |  |  |  |  |  |
ASE Embedded Electronics Inc. [member] | TDK Corporation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ordinary shares acquired |  | $ 6,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
SUMA-USI Electronics Co., Ltd. [member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest in joint venture |  |  |  |  |  |  |  | 49.00% |  |  |  |  |  |  |  |
Investments in joint ventures |  |  |  |  |  |  |  |  | $ 283,236 |  |  |  | $ 9,470 | ¥ 65,170 |  |
SUMA-USI Electronics Co., Ltd. [member] | Cancon Information Industry Co Ltd [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of Investments Accounted for Using Equity Method [line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid in cash for shares | ¥ |  |  |  |  |  |  |  | ¥ 107,800 |  |  |  |  |  |  |  |

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