A semiconductor device includes an active pattern protruding from a substrate and extending in a first direction, first and second gate electrodes intersecting the active pattern in a second direction intersecting the first direction, and a source/drain region disposed on the active pattern between the first and second gate electrodes. The source/drain region includes a first part adjacent to an uppermost surface of the active pattern and provided at a level lower than the uppermost surface of the active pattern, and a second part disposed under the first part so as to be in contact with the first part. A width of the first part along the first direction decreases in a direction away from the substrate, and a width of the second part along the first direction increases in a direction away from the substrate.