Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Summary Of Significant Accounting Policies [Abstract]

Consolidated Entities

b. The consolidated entities as of December 31, 2019 and 2020 were as follows:

			Percentage of ownership (%) as of December 31,
Investor	Subsidiary	Business nature	2019		2020
UMC	UMC GROUP (USA)	IC Sales		100.00		100.00
UMC	UNITED MICROELECTRONICS (EUROPE) B.V.	Marketing support activities		100.00		100.00
UMC	UMC CAPITAL CORP.	Investment holding		100.00		100.00
UMC	GREEN EARTH LIMITED (GE)	Investment holding		100.00		100.00
UMC	TLC CAPITAL CO., LTD. (TLC)	Venture capital		100.00		100.00
UMC	UMC INVESTMENT (SAMOA) LIMITED	Investment holding		100.00		100.00
UMC	FORTUNE VENTURE CAPITAL CORP.    (FORTUNE)	Consulting and planning for venture capital		100.00		100.00
UMC	UMC GROUP JAPAN	IC Sales		100.00		—
UMC	UMC KOREA CO., LTD.	Marketing support activities		100.00		100.00
UMC	OMNI GLOBAL LIMITED (OMNI)	Investment holding		100.00		100.00
UMC	SINO PARAGON LIMITED	Investment holding		100.00		100.00
UMC	BEST ELITE INTERNATIONAL LIMITED (BE)	Investment holding		100.00		100.00
UMC	UNITED SEMICONDUCTOR JAPAN CO., LTD.	Sales and manufacturing of integrated circuits		100.00		100.00
UMC, FORTUNE    and TLC	NEXPOWER TECHNOLOGY CORP.    (NEXPOWER)	Sales and manufacturing of solar power    batteries		93.36		—
UMC and FORTUNE	WAVETEK MICROELECTRONICS    CORPORATION (WAVETEK)	Sales and manufacturing of integrated circuits		80.49		81.40
UMC CAPITAL CORP.	UMC CAPITAL (USA)	Investment holding		100.00		—
TLC	SOARING CAPITAL CORP.	Investment holding		100.00		100.00
SOARING CAPITAL    CORP.	UNITRUTH ADVISOR (SHANGHAI) CO., LTD.	Investment holding and advisory		100.00		100.00
GE	UNITED MICROCHIP CORPORATION	Investment holding		100.00		100.00
FORTUNE	TERA ENERGY DEVELOPMENT CO., LTD.    (TERA ENERGY)	Energy technical services		100.00		100.00
TERA ENERGY	EVERRICH ENERGY INVESTMENT (HK)    LIMITED (EVERRICH-HK)	Investment holding		100.00		100.00
EVERRICH-HK	EVERRICH (SHANDONG) ENERGY CO., LTD.	Solar engineering integrated design services		100.00		100.00
OMNI	UNITED MICROTECHNOLOGY    CORPORATION (NEW YORK)	Research and development		100.00		—
OMNI	UNITED MICROTECHNOLOGY    CORPORATION (CALIFORNIA)	Research and development		100.00		100.00
OMNI	ECP VITA PTE. LTD.	Insurance		100.00		100.00
OMNI	UMC TECHNOLOGY JAPAN CO., LTD.	Semiconductor manufacturing technology    development and consulting services		100.00		100.00
WAVETEK	WAVETEK MICROELECTRONICS    INVESTMENT (SAMOA) LIMITED    (WAVETEK-SAMOA)	Investment holding		100.00		100.00
WAVETEK-SAMOA	WAVETEK MICROELECTRONICS    CORPORATION (USA)	Marketing service		100.00		100.00
BE	INFOSHINE TECHNOLOGY LIMITED    (INFOSHINE)	Investment holding		100.00		100.00
INFOSHINE	OAKWOOD ASSOCIATES LIMITED    (OAKWOOD)	Investment holding		100.00		100.00
OAKWOOD	HEJIAN TECHNOLOGY (SUZHOU)    CO., LTD. (HJ)	Sales and manufacturing of integrated circuits		98.14		99.9985
HJ	UNITEDDS SEMICONDUCTOR (SHANDONG)    CO., LTD.	Integrated circuits design services		100.00		100.00
UNITED MICROCHIP    CORPORATION and HJ	UNITED SEMICONDUCTOR (XIAMEN)    CO., LTD. (USCXM)	Sales and manufacturing of integrated circuits		65.22		67.76

Estimated Useful Lives of Property, Plant and Equipment

Except for land, which is not depreciated, the estimated useful lives of the assets are as follows:

Buildings	7~56 years
Machinery and equipment	6~7 years
Transportation equipment	6~7 years
Furniture and fixtures	3~7 years
Leasehold improvement	The shorter of lease terms or useful lives