There is provided a method for manufacturing a semiconductor device, including: providing a semiconductor substrate having a plurality of openings formed thereon by removing a sacrificial gate; filling the openings with a top metal layer having compressive stress; and performing amorphous doping with respect to the top metal layer in a PMOS device region. Thus, it is possible to effectively improve carrier mobility of an NMOS device, and also to reduce the compressive stress in the PMOS device region to ensure a desired performance of the PMOS device.