Exemplary embodiments provide for fabricating a field effect transistor (FET) with an interface layer for a gate stack using an O3 post treatment. Aspects of the exemplary embodiments include: forming a semiconductor body upon a substrate; cleaning the surface of the semiconductor body; depositing a first dielectric layer on the semiconductor body; performing an O3 treatment that mixes with and penetrates the first dielectric layer and reacts with the semiconductor body to form a new interface layer; and performing gate stack processing, including deposition of a gate electrode.