A semiconductor device according to an example embodiment of the present inventive concept includes a substrate having a first region and a second region horizontally separate from the first region; a first gate line in the first region, the first gate line including a first lower work function layer and a first upper work function layer disposed on the first lower work function layer; and a second gate line including a second lower work function layer in the second region, the second gate line having a width in a first, horizontal direction equal to or narrower than a width of the first gate line in the first direction, wherein an uppermost end of the first upper work function layer and an uppermost end of the second lower work function layer are each located at a vertical level higher than an uppermost end of the first lower work function layer with respect to a second direction perpendicular to the first direction.