We found that the Si 2p photoelectron peak binding energy of a Si substrate covered with a 3 nm thick HfAlOx film increased to a saturation value during X-ray irradiation. This shift towards a higher binding energy indicates an increase in the amount of positive charges in the film, and the density of hole traps is estimated to be significantly higher than that in a SiO2 film. Before Xray irradiation, the interface Fermi level coincided with the valence-band maximum of the Si substrate, which indicates that the Si surface band bends upward. This means that there were negative charges already in the film before X-ray irradiation. Investigating the effects of the interlayer beneath the HfAlOx film on these trapped charges reveals that the observed hole trapping and initial electron trapping are intrinsic to the HfAlOx film. (C) 2004 Elsevier B.V. All rights reserved.