A semiconductor device includes a plurality of channel layers disposed on an active region of a substrate and spaced apart from each other in a first direction, a first gate structure surrounding the plurality of channel layers, first source/drain regions disposed on the active region on both lateral sides of the first gate structure and contacting the plurality of channel layers and spaced apart from each other in a second direction, an element isolation layer disposed on an upper portion of the first gate structure, a semiconductor layer disposed on the element isolation layer and having a vertical region extending in the first direction and including second source/drain regions spaced apart from each other in the first direction, and a second gate structure disposed to surround a portion of the vertical region. The semiconductor device further includes first to fourth contact plugs.