A method for fabricating semiconductor device includes the steps of: forming a first gate structure on a substrate; forming a second gate structure on the substrate and on one side of the first gate structure; forming a third gate structure on the substrate and on another side of the first gate structure; forming source/drain regions adjacent to the second gate structure and the third gate structure; and forming contact plugs to contact the first gate structure, the second gate structure, the third gate structure, and the source/drain regions.