A semiconductor device includes a fin protruding from a substrate and extending in a first direction, source/drain regions on the fin, a recess between the source/drain regions, a device isolation region including a capping layer extending along an inner surface of the recess and a device isolating layer on the capping layer to fill the recess, a dummy gate structure on the device isolation region and including a dummy gate insulating layer, outer spacers on opposite sidewalls of the dummy gate structure, first inner spacers between the dummy gate structure and the outer spacers, and a second inner spacer between the device isolation region and the dummy gate insulating layer.