A semiconductor device is described that includes a substrate, an active region protruding from the substrate and extending in a first direction, a plurality of channel layers disposed on the active region and spaced apart from each other in a direction perpendicular to an upper surface of the substrate, an isolation film disposed between a lowermost channel layer of the plurality of channel layers and the active region, a gate electrode surrounding the plurality of channel layers and extending in a second direction intersecting the first direction, and a source/drain region disposed on at least one side of the gate electrode and connected to each of the plurality of channel layers. The isolation film is disposed on a level higher than a bottom surface of the source/drain region.