Photoemission measurements were performed on metal‐insulator‐silicon structures having thin thermal oxynitride films as the insulator. The results for the sample with the least oxidized nitride film, yield for the energy intervals from the insulator conduction band to the Fermi level of the aluminum and to the valence band of the silicon, the values of 3.3 and 3.6 eV, respectively. The affinity of the insulator as deduced from these values is larger at the silicon interface than at the aluminum interface by 0.8 eV, indicating that the film exhibits a graded energy barrier for electron injection from the electrodes.