A method for fabricating a semiconductor circuit includes obtaining a semiconductor structure having a gate stack of material layers including a high-k dielectric layer; oxidizing in a lateral manner the high-k dielectric layer, such that oxygen content of the high-k dielectric layer is increased first at the sidewalls of the high-k dielectric layer; and completing fabrication of a n-type field effect transistor from the gate stack after laterally oxidizing the high-k dielectric layer of the gate stack.