A semiconductor device includes an insulating layer on a substrate, a channel region on the insulating layer, a gate structure on the insulating layer, the gate structure crossing the channel region, source/drain regions on the insulating layer, the source/drain regions being spaced apart from each other with the gate structure interposed therebetween, the channel region connecting the source/drain regions to each other, and contact plugs connected to the source/drain regions, respectively. The channel region includes a plurality of semiconductor patterns that are vertically spaced apart from each other on the insulating layer, the insulating layer includes first recess regions that are adjacent to the source/drain regions, respectively, and the contact plugs include lower portions provided into the first recess regions, respectively.