A method for fabricating semiconductor device includes the steps of first providing a substrate having a fin-shaped structure thereon, forming a single diffusion break (SDB) structure in the substrate to divide the fin-shaped structure into a first portion and a second portion, and then forming more than one gate structures such as a first gate structure and a second gate structure on the SDB structure. Preferably, each of the first gate structure and the second gate structure overlaps the fin-shaped structure and the SDB structure.