Disclosed is a semiconductor device. The semiconductor device includes a substrate, channel semiconductor patterns vertically stacked and spaced apart from each other on the substrate, a gate electrode running across the channel semiconductor patterns, source/drain regions at opposite sides of the gate electrode, the source/drain regions being connected to the channel semiconductor patterns, and air gaps between the substrate and bottom surfaces of the source/drain regions so that the bottom surfaces of the source/drain regions do not contact the substrate.