We have found definite evidence which proves that radiation damage in SiO2/Si induced by low‐energy electrons is caused by plasmon excitation in SiO2. The SiO2/Si sample was irradiated by accelerated thermoelectrons, and the flat‐band voltage shift, &Dgr;VFB, of the sample was measured by theC‐Vmethod. The effective charge generation yield,Rf, in SiO2/Si was evaluated from the &Dgr;VFBand the electron dose. The effective positive charges were measured inp‐type SiO2/Si, and the effective negative charges were measured inn‐type SiO2/Si. This is because interface states behave like positive charges inp‐type SiO2/Si and negative charges inn‐type SiO2/Si. TheRfinp‐type SiO2/Si oscillated as a function of the incident electron energy of 5–150 eV with several clear peaks. These peaks correspond to the quantum energy of a bulk plasmon or a surface plasmon. Both plasmons decay into electron‐hole pairs. The holes that escape from recombination with the electrons are trapped at the SiO2/Si interface and cause effective positive charges. TheRfwas maximum when the SiO2thickness was 20 nm, independent of the incident electron energy. This is because the plasmon region extends to about 20 nm in SiO2, and the hole‐trapping efficiency is expected to be maximum at a SiO2thickness of 20 nm.