A semiconductor device includes a first transistor having a first threshold voltage, and including first channels, first source/drain layers connected to opposite sidewalls of the first channels, and a first gate structure surrounding the first channels and including a first gate insulation pattern, a first threshold voltage control pattern, and a first workfunction metal pattern sequentially stacked. The semiconductor device includes a second transistor having a second threshold voltage greater than the first threshold voltage, and including second channels, second source/drain layers connected to opposite sidewalls of the second channels, and a second gate structure surrounding the second channels and including a second gate insulation pattern, a second threshold voltage control pattern, and a second workfunction metal pattern sequentially stacked. A thickness of the second threshold voltage control pattern is equal to or less than a thickness of the first threshold voltage control pattern.