AbstractX-ray photoelectron spectroscopy (XPS) technique is employed in situ to quantify changes in the electric dipole formed at the metal/dielectric interface. The proposed method is valid in the particular case of discontinuous metal overlayer in contact with dielectric, and allows one to model metal gate effective work function evolution of metal-oxide-semiconductor (MOS) stack following its treatments in different environments. The obtained results on Au / dielectric (dielectric=HfO2, LaAlO3) corroborate the model that the oxygen vacancies generated in dielectric contribute to the effective work function changes.