A method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate having a region; forming a gate structure on the region of the substrate; forming a raised epitaxial layer in the substrate adjacent to two sides of the gate structure; covering a dielectric layer on the gate structure and the raised epitaxial layer; and using a planarizing process to partially remove the dielectric layer and the gate structure such that the surface of the gate structure is even with the surface of the raised epitaxial layer.