This paper presents the results of investigation on integrity of X-ray/E-beam irradiated thin gate oxides. A large increase of gate oxide leakage current is observed after irradiation on thin gate oxide under X-ray/E-beam lithography conditions. This radiation-induced leakage current (RILC) can be removed by a thermal annealing at 400 degrees C and above, without adverse effect to the oxide integrity. In addition, it is found that ionizing exposures do not significantly affect the breakdown and quasi-breakdown characteristics in ultra-thin oxide. (C) 2000 Elsevier Science Ltd. All rights reserved.