The electronic properties of an n-Si(111) surface during the electrochemical H termination process are investigated by the use of the large signal surface photovoltage technique. A strong decrease of the density of interface states up to 2 10(11) eV(-1) cm(-2) and the development of a positive fixed charge at the interface is observed in connection with a decrease of the oxidation state of surface Si atoms. The results are interpreted by surface smoothing concurrent with the hydrogenation of the surface.