There is disclosed a method for manufacturing a semiconductor device comprising two opposite types of MOSFETs formed on one semiconductor substrate, the method comprising: forming a portion of the MOSFET on the semiconductor substrate, said portion of said MOSFET comprising source/drains regions located in the semiconductor substrate, a dummy gate stack located between the source/drain region and above the semiconductor substrate and a gate spacer surrounding the dummy gate stack; removing the dummy gate stack of said MOSFET to form a gate opening which exposes the surface of the semiconductor substrate; forming an interfacial oxide layer on the exposed surface of the semiconductor structure; forming a high-K gate dielectric on the interfacial oxide layer within the gate opening; forming a first metal gate layer on the high-K gate dielectric; implanting doping ions in the first metal gate layer; forming a second metal gate layer on the first metal gate layer to fill up the gate opening; and annealing to diffuse and accumulate the doping ions at an upper interface between the high-K gate dielectric and the first metal gate layer and at a lower interface between the high-K gate dielectric and the interfacial oxide, and generating an electric dipole at the lower interface between the high-K gate dielectric and the interfacial oxide by interfacial reaction.