A semiconductor device including a substrate; a gate structure on the substrate; a gate spacer on a sidewall of the gate structure; and a polishing stop pattern on the gate structure and the gate spacer, the polishing stop pattern including a first portion covering an upper surface of the gate structure and an upper surface of the gate spacer; and a second portion extending from the first portion in a vertical direction substantially perpendicular to an upper surface of the substrate, wherein an upper surface of a central portion of the first portion of the polishing stop pattern is higher than an upper surface of an edge portion of the first portion thereof, and the upper surface of the central portion of the first portion of the polishing stop pattern is substantially coplanar with an upper surface of the second portion thereof.