A semiconductor device includes a substrate having a first region and a second region, a plurality of first gate structures in the first region, the first gate structures being spaced apart from each other by a first distance, a plurality of second gate structures in the second region, the second gate structures being spaced apart from each other by a second distance, a first spacer on sidewalls of the first gate structures, a dielectric layer on the first spacer, a second spacer on sidewalls of the second gate structures, and a third spacer on the second spacer.