A semiconductor device includes a p-type metal oxide semiconductor device (PMOS) and an n-type metal oxide semiconductor device (NMOS) disposed over a substrate. The PMOS has a first gate structure located on the substrate, a carbon doped n-type well disposed under the first gate structure, a first channel region disposed in the carbon doped n-type well, and activated first source/drain regions disposed on opposite sides of the first channel region. The NMOS has a second gate structure located on the substrate, a carbon doped p-type well disposed under the second gate structure, a second channel region disposed in the carbon doped p-type well, and activated second source/drain regions disposed on opposite sides of the second channel region.