Abstract: A semiconductor device including a substrate including a first and second region; a first active region formed in an upper portion of the substrate in the first region; a second active region formed in an upper portion of the substrate in the second region; a first gate structure extending across the first active region, having a first gate length, and including a first high-k dielectric layer, a first lower metal layer, and a first upper metal layer; a second gate structure extending across the second active region, having a second gate length, and including a second high-k dielectric layer, a second lower metal layer having at least one metal layer, and a second upper metal layer; and spacers at sides of each of the first and second gate structures, a cross section of each of the first and second high-k dielectric layers has a U-shape, a cross section of each of the first and second lower metal layers has a U-shape, the first and second lower metal layers covering bottom surfaces and inner side surfaces of