N-type GaN exhibits upward, near-surface band bending that can be decreased by generating a surface photovoltage (SPV). Fitting SPV measurements with a thermionic model based on the emission of charge carriers over the nearsurface barrier provides information about the band bending in dark. We have studied the temperature dependent SPV behavior from a Si-doped, n-type GaN sample grown by hydride vapor phase epitaxy in order to determine how the magnitude of band bending changes at higher temperatures. We have measured the effect of temperature and oxygen on the steady-state SPV behavior, where oxygen is photo-adsorbed on the surface under band-to-band illumination in an air/oxygen ambient more efficiently at higher temperatures. As predicted, the intensity-dependent SPV measurements performed at temperatures between 295 and 500 K exhibit a decrease in the maximum SPV with increasing temperature. When illumination ceases, the band bending then begins to restore to its dark value with a rate proportional to the sample temperature, which also fits a thermionic model.