A method of manufacturing a semiconductor device, including forming a plurality of gate structures on a substrate, the gate structures each including a hard mask pattern stacked on a gate conductive pattern, forming an insulating layer pattern between the gate structures at least partially exposing a top surface of the hard mask pattern, forming a trench that exposes at least a top surface of the gate conductive pattern by selectively removing the hard mask pattern, and forming a silicide layer on the exposed gate conductive pattern.