A semiconductor device is disclosed. The device includes a substrate including an active region defined by a device isolation layer, a fin pattern protruding from the substrate and extending in a first direction, the fin pattern including a gate fin region and a source/drain fin region, a gate pattern disposed on the gate fin region to extend in a second direction crossing the first direction, and a source/drain portion provided on a sidewall of the source/drain fin region. When measured in the second direction, a width of the source/drain fin region is different from a width in the second direction of the gate fin region.