A method for fabricating semiconductor device includes the steps of: 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; forming a first gate structure on the SDB structure; forming an interlayer dielectric (ILD) layer on the first gate structure; removing the first gate structure to form a first recess; and forming a dielectric layer in the first recess.