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Pensions - Additional Information (Detail)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
TWD ($)
Unit
Dec. 31, 2023
TWD ($)
Dec. 31, 2022
TWD ($)
Disclosure of defined benefit plans [Line Items]      
Weighted average duration of defined benefit obligation 9 years 3 months 18 days    
Defined benefit plans expected contribution | $ $ 27,600    
ChipMOS Shanghai [Member]      
Disclosure of defined benefit plans [Line Items]      
Employer contribution percentage 16.00% 16.00% 16.00%
Pension costs under defined contribution pension plans | $ $ 715 $ 604 $ 380
Defined benefit pension plan [Member]      
Disclosure of defined benefit plans [Line Items]      
Number of units accrued in first tranche | Unit 2    
Duration of first tranche first 15 years    
Number of units accrued in second tranche | Unit 1    
Duration of second tranche Thereafter 15 years    
Maximum number of units accruable under the pension plan | Unit 45    
Benefit measurement period 6 months    
Employer contribution percentage 2.00%    
Defined contribution pension plan [member]      
Disclosure of defined benefit plans [Line Items]      
Employer contribution percentage 6.00%    
Pension costs under defined contribution pension plans | $ $ 211,985 $ 190,913 $ 201,606