A semiconductor device may include a substrate, an active pattern extended in a first horizontal direction on the substrate, a plurality of nanosheets stacked and spaced apart from each other in a vertical direction on the active pattern, a gate electrode extended in a second horizontal direction different from the first horizontal direction on the active pattern, the gate electrode surrounding the plurality of nanosheets, a source/drain region on both sides of the plurality of nanosheets in the first horizontal direction on the active pattern, a gate insulating layer between the plurality of nanosheets and the gate electrode, and a doping layer between the plurality of nanosheets and the gate insulating layer, the doping layer including silicon (Si) or silicon germanium (SiGe) and doped with a doping material, at least a portion of the doping layer overlapping an uppermost nanosheet of the plurality of nanosheets in the first horizontal direction.