Provided are semiconductor devices and methods of manufacturing the same. A semiconductor device may include a source, a drain, a semiconductor element between the source and the drain, and a graphene layer that is provided on the source and the semiconductor element and is spaced apart from the drain. Surfaces of the source and the drain are substantially co-planar with a surface of the semiconductor element. The semiconductor element may be spaced apart from the source and may contact the drain. The graphene layer may have a planar structure. A gate insulating layer and a gate may be provided on the graphene layer. The semiconductor device may be a transistor. The semiconductor device may have a barristor structure. The semiconductor device may be a planar type graphene barristor.