A semiconductor device includes a gate structure extending in a second direction on a substrate, a source/drain layer disposed on a portion of the substrate adjacent the gate structure in a first direction crossing the second direction, a first conductive contact plug on the gate structure, and a second contact plug structure disposed on the source/drain layer. The second contact plug structure includes a second conductive contact plug and an insulation pattern, and the second conductive contact plug and the insulation pattern are disposed in the second direction and contact each other. The first conductive contact plug and the insulation pattern are adjacent to each other in the first direction. The first and second conductive contact plugs are spaced apart from each other.