The recent improvement of GaN material quality launched new perspective for its application in power devices. However, ion-implanted guard-ring edge terminations, necessary to improve the breakdown voltage, are not well developed as in SiC technology. Indeed, the effects of high-temperature annealing, required for the electrical activation of the implanted species in GaN, on the electrical behaviour of Schottky contact was not reported. In this work, the influence of high temperature annealing (1150-1200°C) on the surface morphology of GaN and on the electrical behaviour of Schottky contact was studied. Although the morphology of GaN surface did not substantially change after annealing, a worsening of the electrical behaviour of Schottky contact was observed. This latter was ascribed to the formation of a high density of interface states after annealing.