A semiconductor device includes first and second active regions on a substrate, an element isolation layer between the first and second active regions, a dummy gate line, dummy gate spacers at opposite side walls of the dummy gate line, and a dummy gate capping layer on the dummy gate line and. An upper surface of the element isolation layer is proximate to an upper surface of the substrate in relation to an upper end of the first active region in a vertical direction. The dummy gate line includes a horizontal section extending on the first active region to the element isolation layer in a horizontal direction, and a vertical section extending downwards from the horizontal section along a side wall of the first active region, the dummy gate line having an L shape, a vertical thickness of the horizontal section being smaller than a vertical thickness of the vertical section.