A semiconductor device includes a single diffusion break (SDB) structure dividing a fin-shaped structure into a first portion and a second portion, an isolation structure on the SDB structure, a first spacer adjacent to the isolation structure, a metal gate adjacent to the isolation structure, a shallow trench isolation (STI around the fin-shaped structure, and a second isolation structure on the STI. Preferably, a top surface of the first spacer is lower than a top surface of the isolation structure and a bottom surface of the first spacer is lower than a bottom surface of the metal gate.