The paper describes the application of X-ray photoelectron spectroscopy (XPS) based method to quantify changes in the electric dipole formed at the metal/dielectric interface following heat treatments of metal–oxide–semiconductor (MOS) stack in different environments. The presented results on Me (Me = Au, Ni)/dielectric (dielectric = HfO2, LaAlO3) evidence the oxygen vacancies generated in dielectric contribute to the effective work function changes.