We report a technique to characterize carrier-trapping phenomena in SiO2 by measuring the Si 2p core-level energy of Si substrates covered with thin SiO2 layers as a function of x-ray irradiation time. It is found that the Si 2p peak energy, which corresponds to the band bending at the SiO2/Si interface, changes as the x-ray irradiation time increases. We attribute this to carrier-trapping phenomena in SiO2. By using this technique, it is found that the carrier-trapping phenomena differ remarkably among several chemical oxides. We also discuss the atomic structure of the traps that cause the trapping phenomena. © 1999 American Institute of Physics.