Here we report on high field transport in GaN based on the rigid ion model of theelectron–phonon interaction within the cellular Monte Carlo (CMC) approach. Usingthe rigid pseudo-ion method for the cubic zinc-blende and hexagonal wurtzitestructures, the anisotropic deformation potentials are derived from the electronicstructure, the atomic pseudopotential and the full phonon dispersion and eigenvectorsfor both acoustic and optical modes. Several different electronic structure andlattice dynamics models are compared, as well as different models for theinterpolation of the atomic pseudopotentials required in the rigid pseudo-ionmethod. Piezoelectric as well as anisotropic polar optical phonon scattering isaccounted for as well. In terms of high field transport, the peak velocity is primarilydetermined by deformation potential scattering described through the rigid pseudo-ionmodel. The calculated velocity is compared with experimental data from pulsedI–V measurements. Good agreement is found using the rigid ion model to the measuredvelocity–field characteristics with the inclusion of dislocation and ionized impurityscattering. The crystal orientation of the electric field is investigated, where very littledifference is observed in the velocity–field characteristics. We simulate the effects ofnonequilibrium hot phonons on the energy relaxation as well, using a detailed balancebetween emission and absorption during the simulation, and an anharmonic decay of LOphonons to acoustic phonons, as reported previously. Nonequilibrium phonons are shown toresult in a significant degradation of the velocity–field characteristics for high carrierdensities, such as those encountered at the AlGaN/GaN interface due to polarizationeffects.