We present velocity-field simulations of n-doped, wurtzite-phase GaN for temperatures between 77 and 1000 K using an ensemble Monte Carlo technique. A three-valley model of the band structure is assumed, and the ionized impurity, polar optical phonon, acoustic phonon, piezoelectric, and intervally scattering mechanisms are considered. Electron degeneracy and heating are also accounted for. Properties of the two dimensional electron gas in AlGaN/GaN heterostructures are also estimated by performing simulations on bulk GaN in which the electron concentration exceeds the ionized donor concentration by factors of ten to one hundred. The simulations predict that peak steady-state drift velocities ranging from 3.3×107 to 2.1×107 cm/s for temperatures between 77 and 1000 K can be achieved in both the two dimensional electron gas and in the bulk material with an ionized donor concentration of 1016 cm-3. Furthermore, the simulations predict that the two-dimensional electron gas in GaN will exhibit a low-field mobility an order of magnitude greater than the bulk material, in agreement with experimental results. © 1997 American Institute of Physics.