Temperature-dependent reverse-bias current-voltage data obtained by Miller etal [Appl. Phys. Lett. 84, 535 (2004)] for Schottky diodes fabricated on n-GaN are reinterpreted in terms of a phonon-assisted tunneling model. It is shown that the temperature dependence of the reverse-bias leakage current may be caused by the temperature dependence of the electron tunneling rate from traps in the metal-semiconductor interface to the conduction band of the semiconductor. A good fit of the experimental data with this theoretical model is obtained in the entire temperature range from 80 to 400 K, when an effective mass of 0.222me and a phonon energy of 70 meV are used for the calculation. The reverse current-voltage data for GaN diodes are also explained on the basis of this model.