To analyze defect-assisted elastic tunneling currents through ultrathin SiO2 gate oxides in metal-oxide semiconductor field-effect transistors (MOSFETs), we have combined semiempirical microscopic tight-binding calculations with full-band Monte Carlo transport simulations. Two prototypical devices with channel lengths of 50 and 90 nm were considered. We find that defects having an area density larger than 10(11) cm(-2) can enhance tunneling currents by several orders of magnitude in both devices. Resonant tunneling effects are predicted to be more pronounced for thicker oxides. For oxides thinner than 2 nm, hot electrons are unlikely to dominate gate leakage currents in the presence of defects. (C) 2002 Elsevier Science Ltd. All rights reserved.