A semiconductor device is provided. The semiconductor device includes an active pattern extending in a first horizontal direction, a plurality of lower nanosheets stacked on the active pattern and spaced apart from one another in a vertical direction, a separation layer on the plurality of lower nanosheets, a plurality of upper nanosheets stacked on the separation layer and spaced apart from one another in the vertical direction, a gate electrode extending on the active pattern in a second horizontal direction, the gate electrode surrounding each of the plurality of lower nanosheets, the separation layer and the plurality of upper nanosheets, and a first conductive layer between the gate electrode and each of a top surface and a bottom surface of the plurality of upper nanosheets. The first conductive layer is not between the gate electrode and sidewalls of the plurality of upper nanosheets.