A semiconductor device includes a semiconductor substrate, at least a first fin structure, at least a second fin structure, a first gate, a second gate, a first source/drain region and a second source/drain region. The semiconductor substrate has at least a first active region to dispose the first fin structure and at least a second active region to dispose the second fin structure. The first/second fin structure partially overlapped by the first/second gate has a first/second stress, and the first stress and the second stress are different from each other. The first/second source/drain region is disposed in the first/second fin structure at two sides of the first/second gate.