Semiconductor devices may include a substrate, an active region that is on the substrate and extends in a first direction, a gate structure that traverses the active region and extends in a second direction that may be different from the first direction, a source/drain region on the active region adjacent a side of the gate structure, an insulating layer on the substrate, the gate structure and the source/drain region, and a contact structure that is in the insulating layer and is connected to the source/drain region. In the source/drain region, a contact region that is in contact with the contact structure includes first and second side regions spaced apart from each other in the second direction and a central region between the first and second side regions, and at least one of the first and second side regions may include a recess.