The charge transport mechanism in amorphous silicon nitride, Si3N4, was experimentally examined to compare measured data with theoretical calculations made within the Frenkel model and the multi-phonon model of trap ionization. A good agreement between the experimental data and theoretical predictions could be achieved assuming the multi-phonon mechanism to be in effect. The widely accepted Frenkel model, although capable of explaining the measured data, fails to yield realistic values of the electron tunnel mass and attempt-to-escape factor. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.