We have developed an XPS time-dependent measurement technique with which we can address serious reliability issues in metal-oxide-semiconductor field-effect transistors (MOSFETs). By using this technique, we determined the density of hole traps in ultrathin SiO2 films without making electrodes for electrical measurements. In this paper, we demonstrate a new application of this method to analysis of the electron trapping and interface states generation during electron-beam irradiation. We found that the Si 2p peak binding energy of a n-type Si substrate covered with a SiO2 film (0.8 nm) decreases to a saturation value during electron-beam (0.5 eV: only electron injection case) irradiation. From the shift of the Si 2p peak binding energy, we were able to obtain the electron trap density of the SiO2 film. On the other hand, the binding energy first increases, then decreases to a saturation energy, smaller than the initial value, during electron-beam (6 eV: both electron and hole injection case) irradiation. The complex phenomena are discussed in connection with interface states generation at SiO2/Si interfaces. (C) 2004 Elsevier B.V. All rights reserved.