A method for fabricating a semiconductor device comprising a gate stack of a gate dielectric and a gate electrode, the method including forming a gate dielectric layer over a semiconductor substrate the gate dielectric layer being a metal oxide or semimetal oxide having a first electronegativity; forming a dielectric VT adjustment layer, the dielectric VT adjustment layer being a metal oxide or semimetal oxide having a second electronegativity; and forming a gate electrode over the gate dielectric layer and the VT adjustment layer; wherein the Effective Work Function of said gate stack is tuned to a desired value by tuning the thickness and composition of the dielectric VT adjustment layer and wherein the second electronegativity value is higher than both the first electronegativity value and the electronegativity of Al2O3.