We have characterized the carrier-trapping phenomena in ultrathin (1.3–3.5 nm) SiO2 films (practical used thermal oxide and oxynitride) by using x-ray photoelectron spectroscopy time-dependent measurements. It was found that the net amount of hole traps in the ultrathin oxynitride is smaller than that in the ultrathin thermal oxide. This result is consistent with the previously reported results for the thick thermal oxide and oxynitride using conventional electrical measurements. We consider what is responsible for the contribution to the formation of hole traps. © 2000 American Institute of Physics.