A method for fabricating semiconductor device includes the steps of first providing a substrate, forming a gate structure on the substrate, forming a hard mask on the substrate and the gate structure, patterning the hard mask to form trenches exposing part of the substrate, and forming raised epitaxial layers in the trenches. Preferably, the gate structure is extended along a first direction on the substrate and the raised epitaxial layers are elongated along a second direction adjacent to two sides of the gate structure.