The inventive concept relates to a semiconductor device and a method for fabricating the same. The semiconductor device comprises active patterns protruding from a substrate, an interlayer dielectric layer disposed on the substrate and including grooves exposing the active patterns, and gate electrodes in the grooves. The grooves include a first groove having a first width and a second groove having a second width greater than the first width. The gate electrodes include a first gate electrode in the first groove, and a second gate electrode in the second groove. Each of the first and second gate electrodes includes a first work function conductive pattern on a bottom surface and sidewalls of corresponding one of the first and second grooves, and a second work function conductive pattern on the first work function conductive pattern.