A semiconductor device includes a substrate having a first area and a second area adjacent to the first area, a first silicon layer provided on the substrate in the first area, a relaxed layer which is provided on the substrate in the second area and which has a lattice constant greater than a lattice constant of the first silicon layer, and a strained-Si layer which is provided on the relaxed layer and which has a lattice constant substantially equivalent to the lattice constant of the relaxed layer.