A method of manufacturing a semiconductor device, the method including: forming, in a first region of a substrate, an active fin and a sacrificial gate structure intersecting the active fin; forming a first spacer and a second spacer on the substrate to cover the sacrificial gate structure; forming a mask in a second region of the substrate to expose the first region of the substrate; removing the second spacer from the first spacer in the first region of the substrate by using the mask; forming recesses at opposite sides of the sacrificial gate structure by removing portions of the active fin; forming a source and a drain in the recesses; and forming an etch-stop layer to cover both sidewalls of the sacrificial gate structure and a top surfaces of the source and drain.