A metal gate/high-k dielectric semiconductor device provides an NMOS gate structure and a PMOS gate structure formed on a semiconductor substrate. The NMOS gate structure includes a high-k gate dielectric treated with a dopant impurity such as La and the high-k gate dielectric material of the PMOS gate structure is deficient of this dopant impurity and further includes a work function tuning layer over the high-k gate dielectric. A process for simultaneously forming the NMOS and PMOS gate structures includes forming the high-k gate dielectric material, and the work function tuning layer thereover, then selectively removing the work function tuning layer from the NMOS region and carrying out a plasma treatment to selectively dope the high-k gate dielectric material in the NMOS region with a dopant impurity while the high-k gate dielectric in the PMOS region is substantially free of the dopant impurity.