A method for fabricating a semiconductor device is provided. In the method, a bulb type recess is formed on a semiconductor substrate in an active region. A gate insulating film is formed over the semiconductor substrate and on a surface of the recess. A first polysilicon layer is formed over the gate insulating film. A silicon-on-dielectric (“SOD”) barrier film is formed on the first polysilicon layer at a lower part of the recess. A second polysilicon layer is formed over the semiconductor substrate and filling the recess. Impurity ions are injected into the second polysilicon layer. An annealing process is performed on the semiconductor substrate. A metal layer and a gate hard mask layer is formed and patterned over the second polysilicon layer to form a gate including the SOD barrier film.