A semiconductor device includes an active region extending on a substrate in a first direction and including an impurity region, a plurality of channel layers vertically spaced apart from each other on the active region, a gate structure extending on the substrate in a second direction to intersect the active region and the plurality of channel layers, and surrounding the plurality of channel layers, a source/drain region disposed on the active region on at least one side of the gate structure and in contact with the plurality of channel layers, a barrier layer including a first barrier layer spaced apart from an upper surface of the active region and being disposed in the active region, and second barrier layers respectively disposed below the plurality of channel layers, and a contact plug connected to the source/drain region.