An N-type MOSFET and a method for manufacturing the same are disclosed. In one aspect, the method comprises forming source/drain regions in a semiconductor substrate. The method also includes forming an interfacial oxide layer on the semiconductor substrate. The method also includes forming a high-k gate dielectric layer on the interfacial oxide layer. The method also includes forming a first metal gate layer on the high-k gate dielectric layer. The method also includes implanting dopants into the first metal gate layer through conformal doping. The method also includes annealing a gate stack to change an effective work function of the gate stack which includes the first metal gate layer, the high-k gate dielectric, and the interfacial oxide layer.