A method of forming agate structure having an improved electric characteristic is disclosed. A gate insulating layer is formed on a substrate and a metal layer is formed on the gate insulating layer. Then, an amorphous silicon layer is formed on the metal layer by a physical vapor deposition (PVD) process. An impurity doped polysilicon layer is formed on the amorphous silicon layer. Formation of an oxide layer at an interface between the amorphous silicon layer and the metal layer may be prevented.