1. A method of forming a replacement gate stack for a p-type field-effect transistor (pFET) and an n-type field-effect transistor (nFET), the method comprising: forming an interfacial layer in a first opening in a pFET region and a second opening in an nFET region, each opening being in a dielectric layer in the pFET region and the nFET region; forming a high-k layer over the interfacial layer in each of the first and second openings; forming a wetting layer over the high-k layer in each of the first and second openings; forming a first metal layer in each of the first and second openings, the first metal layer including tungsten; and forming a first gate electrode layer over the first metal layer in each of the first and second openings to substantially fill each of the first and second openings, thereby forming a first replacement gate stack over the pFET region and a second replacement gate stack over the nFET region.