Energy barrier heights at the interfaces of metal–silicon nitride–silicon structures have been measured by internal photoemission as a function of metal electrode material and substrate doping. These measurements have been interpreted in terms of a dominant hole internal photoemission mechanism. Hole energy barriers from the Au, Al, or Mg Fermi level and the Si valence band to the Si3N4valence band were found to be 1.9±0.1, 3.0±0.1, 4.0±0.1, and 2.1±0.1 eV, respectively.