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The electron mobility of zincblende (ZB) and wurtzite (WZ) structures of n-type GaN is investigated as a function of both temperature and donor concentration. Numerical calculations of the mobility are carried out in a temperature range from 10 K up to 400 K and donor doping concentrations from 10 19 m -3 to 10 27 m -3 . Elastic types of scattering mechanisms are considered. These types include ionized impurity scattering, neutral impurity scattering, deformation potential acoustic phonons scattering and piezoelectric potential scattering. The electron drift mobility versus temperature shows peak behavior for both zincblende and wurtzite GaN structures. Below approximately 120/140 K (for ZB and WZ GaN respectively), the mobility increases when the temperature is increased. In this temperature range, the ionized impurity scattering is assumed to be the dominant scattering mechanism. Above 120/140 K, the mobility is lowered down by raising the temperature. In this regime, the lattice scattering is considered to be the dominant mechanism. The variation of the electron drift mobility with donor concentration at room temperature shows a continuous decrease with the increase of impurity doping concentration. This is probably due to Coulomb scattering present particularly at low temperatures.