This work presents experimental and computational investigations on the physical mechanisms of SILC. Carrier separation measurements are carried out on MOS samples with oxide thickness 6 -8 nm, highlighting the electron and hole contributions to the SILC. We have investigated the relation between these components by means of timerelaxation. It is found that a linear relationship holds between electron SILC and hole SILC, measured at different times after the initial high-field stress. The same linearity has been observed for increasing fluences of injected electrons, at fixed stressing field. A correlation between electron and hole SILC is found also from a comparison between carrier separation data obtained in n f -and p+-polysilicon devices. These experimental data entails that hole SILC is due to a recombination current.As a result of these experimental findings, a new model for the SILC is developed. This model is based on trapassisted tunneling, but also accounts for hole tunneling and includes Shockley-Hall-Read recombination process in the bulk oxide as a new leakage mechanism. Simulations in the oxide thickness range 5.9 -8.2 nm show excellent agreement with I -V measurements and carrierseparation data. The resulting defect concentration scales with the oxide thickness, in agreement with published results. The energy distribution of defects responsible for the steady-state leakage is located 0.7 -1.3 eV below the Si conduction-band minimum. Capture cross sections of cm2 have been assumed for electrons and holes respectively, compatible with a donor charge state of the SILC-related defect centers.Simulations are finally shown for oxide thickness to, = 2.8 nm. The mechanism of recombination in the bulk oxide accounts very well for the observation of low-voltage SILC in ultrathin oxide, showing the effectiveness of the proposed SILC model. and