A method for fabricating semiconductor device includes the steps of: providing a substrate having a first region and a second region; forming a first fin-shaped structure on the first region and a second fin-shaped structure on the second region; forming a shallow trench isolation (STI) around the first fin-shaped structure and the second fin-shaped structure; forming a mask layer on the first fin-shaped structure; and performing a first anneal process so that the first fin-shaped structure and the second fin-shaped structure comprise different radius of curvature.