A semiconductor device includes a substrate; protruding portions extending in parallel to each other on the substrate; nanowires provided on the protruding portions and separated from each other; gate electrodes provided on the substrate and surrounding the nanowires; source/drain regions provided on the protruding portions and sides of each of the gate electrodes, the source/drain regions being in contact with the nanowires; and first voids provided between the source/drain regions and the protruding portions.