A method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate having a gate structure thereon, a first hard mask atop the gate structure, and an interlayer dielectric (ILD) layer around the gate structure and the first hard mask; removing part of the first hard mask; forming a second hard mask layer on the first hard mask and the ILD layer; and planarizing part of the second hard mask layer to form a second hard mask on the first hard mask.