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, and forming a shallow trench isolation (STI) around the first fin-shaped structure and the second fin-shaped structure. Preferably, the first fin-shaped structure and the second fin-shaped structure comprise different radius of curvature and a center of curvature of the first fin-shaped structure is lower than a top surface of the STI and a center of curvature of the second fin-shaped structure is higher than the top surface of the STI.