A semiconductor device is provided. The semiconductor device includes: a substrate with an active region extending in a first direction; an element isolation layer, adjacent to the active region, in the substrate; a gate electrode on the substrate and extending in a second direction which crosses the first direction; a plurality of channel layers on the active region, spaced apart from each other along a third direction perpendicular to an upper surface of the substrate, and surrounded by the gate electrode; and a source/drain region provided in a recess of the active region adjacent to the gate electrode, and connected to the plurality of channel layers. In the first direction, the gate electrode has a first length on the active region and a second length, greater than the first length, on the element isolation layer.