Admittance (ac) measurements were carried out to determine the interface trap density (D-it) as a function of energy E in the Si bandgap at interfaces of Si with different insulating oxides (Al2O3, ZrO2, HfO2). The results are compared to those of the conventional thermal SiO2/Si interface. The results show that a significant portion of the interface trap density in the as-deposited and de-hydrogenated samples is related to the amphoteric Si dangling bond defects (P-b0 -centers). The D-it is much enhanced for the Al-containing insulators as compared to Si/SiO2 but can be reduced by annealing in O-2. As to annealing in H-2, efficient passivation of P-b0 centers by hydrogen is achieved for Si/ZrO2 and Si/HfO2 interfaces, yet it fails for Si/Al-containing oxide entities. Among the insulators studied, the results suggest HfO2 to be the best choice of an alternative insulator. (c) 2004 Elsevier Ltd. All rights reserved.