A semiconductor device has a substrate, a gate dielectric layer, and a metal gate electrode on the gate dielectric layer. The gate dielectric layer includes an oxide layer having a dielectric constant (k) greater than 4, and silicon concentrated at interfaces of the oxide layer with the substrate and with the metal gate electrode. A method of fabricating a semiconductor device includes forming a removable gate over a substrate with a gate dielectric layer between the removable gate and the substrate, forming a dielectric layer over the substrate and exposing an upper surface of the removable gate, removing the removable gate leaving an opening in the dielectric layer, forming a protective layer on the gate dielectric layer and lining the opening, and forming a metal gate electrode in the opening. The protective layer has a graded composition between the gate dielectric layer and the metal gate electrode.