The effect of electron and ion beam irradiation on the SiL vvAuger spectra of SiO2, Si3N4and Si-oxynitride films was measured by the relative intensity of the 92 eV signal, characteristic for the formation of “free” silicon during irradiation. While in Si-oxynitride (O/N = 0.37) the beam effects were almost negligible, some damage was found in Si3N4, but SiO2appeared to be extremely sensitive for electron and ion beam irradiation. By low energy electron loss spectroscopy (ELS) of ion bombarded SiO2and Si3N4films new electron states due to broken Si-O and Si-N bonds could be determined within the band gap of the insulators. The measured energy losses were interpreted by means of electron energy level schemes of the amorphous films.