The metal/oxide/n-silicon tunneling diodes with hydrogen (deuterium) passivated Si/SiO2 interface are stressed under hole-injection conditions to investigate the mechanism of gate oxide degradation. Although the isotope effect on soft breakdown was previously observed in the deuterium-annealed metal/oxide/p-silicon devices, no isotope effect on the oxide soft breakdown was observed in the metal/oxide/n-silicon devices. However, the time evolution of electroluminescence indeed shows the isotope effect on the interface states density at the Si/SiO2 interface of the metal/oxide/nsilicon devices. This suggests that there is an isotope effect on the hydrogen (deuterium)-release at Si/SiO2 interface under hole current stress from the gate electrodes, but the released hydrogen moves to the bulk Si (not oxide) due to the direction of the electric field. This can explain that the isotope effect is observed in the clectroluminescence measurement, but not in the soft breakdown measurement. The hydrogen released to the bulk Si is not responsible for the soft breakdown, and the tunneling-hole-induced traps in the oxide may be responsible. (C) 2003 Published by Elsevier Science Ltd.