A semiconductor device includes a source/drain pattern disposed on a substrate and a source/drain contact connected to the source/drain pattern. The source/drain contact includes a lower contact structure extending in a first direction and an upper contact structure protruding from the lower contact structure. The upper contact structure includes a first sidewall and a second sidewall facing away from each other in the first direction. The first sidewall of the upper contact structure includes a plurality of first sub-sidewalls, and each of the first sub-sidewalls includes a concave surface.