An analysis of the tunnelling conduction mechanisms through thin films of thermally grown SiO2 is used to characterize the interface states in AlSiO2Si (n) structures which were fabricated from an Si (n) epitaxial layer grown on a p+ -substrate, oriented 〈111〉. The thin oxide layer (3-4 nm) was obtained by surface oxidation in dry oxygen and the aluminium was deposited by thermal evaporation. Measurements of the reverse saturation current have been performed for different temperatures (20-83° C). This current temperature sensitivity allows us to obtain the most effective trap states for trap assisted tunnelling, which has been proved to be the main conduction mechanism in the analysed structures. The advantage of the proposed method is that it provides results independently of the critical parameters in tunnelling measurements, i.e. oxide thickness and density of interface states. So the oxide roughness has no influence in the energy of the trap states. Finally, by means of the trap assisted barrier height the trap density is also obtained. © 1984.