A semiconductor device includes a multi-channel active pattern, a plurality of gate structures on the multi-channel active pattern and spaced apart from each other in a first direction, the plurality of gate structures including a gate electrode that extends in a second direction different from the first direction, a source/drain recess between the adjacent gate structures, and a source/drain pattern on the multi-channel active pattern in the source/drain recess, wherein the source/drain pattern includes: a semiconductor liner layer including silicon-germanium and extending along the source/drain recess, a semiconductor filling layer including silicon-germanium on the semiconductor liner layer, and at least one or more semiconductor insertion layers between the semiconductor liner layer and the semiconductor filling layer, and wherein the at least one or more semiconductor insertion layers have a saddle structure.