The concentrations ofE’centers (ESR‐active oxygen vacancies) produced by 30–160 keV electron irradiation have been measured in thermal SiO2films at doses far exceeding any previously reported. The dependences of these concentrations on electron energy and fluence were measured in both steam‐grown and dry oxides. Results indicated that ionization rather than atomic displacement is the predominant formation mechanism. Significant differences in dose dependence were found between oxide types, reflecting the role of hydrogen in damage annealing.