A semiconductor device includes: an active pattern including a lower pattern and sheet patterns spaced apart from the lower pattern in a first direction; gate structures being separate in a second direction on the lower pattern. The gate structure includes a gate electrode and a gate insulating layer; a source/drain recess between the gate structures adjacent to each other; and a source/drain pattern filling the source/drain recess. The source/drain pattern includes: a first epitaxial region extended along a sidewall and a bottom surface of the source/drain recess, a second epitaxial region on the first epitaxial insertion epitaxial regions that are in contact with the first epitaxial region. The respective insertion epitaxial regions are spaced apart from each other and include silicon germanium. The first epitaxial region is disposed between the second epitaxial region and the insertion epitaxial region.