Based on carrier-separation measurement on pMOSFET, we show the existence of hole trap-assisted tunneling (HTAT) current after 10 keV X-ray irradiation on ultrathin gate oxide. The characteristics of this current have been studied in detail and compared with the corresponding current due to electrical stress. No essential difference is found between the HTAT currents due to ionizing radiation and electrical stress. The results indicate that these two currents have similar origin. (C) 2000 Elsevier Science Ltd. All rights reserved.