An integrated circuit device includes a fin-type active region extending on a substrate in a first direction parallel to a top surface of the substrate; a gate structure extending on the fin-type active region and extending in a second direction parallel to the top surface of the substrate and different from the first direction; and source/drain regions in a recess region extending from one side of the gate structure into the fin-type active region, the source/drain regions including an upper semiconductor layer on an inner wall of the recess region, having a first impurity concentration, and including a gap; and a gap-fill semiconductor layer, which fills the gap and has a second impurity concentration that is greater than the first impurity concentration.