Effects of thermal annealing on the morphology of the AlxGa(1-x)N films with two different high Al-contents (x=0.43 and 0.52) have been investigated by atomic force microscopy (AFM). The annealing treatments were performed in a nitrogen (N2) gas ambient as short-time (4 min) and long-time (30 min). Firstly, the films were annealed as short-time in the range of 800-950 °C in steps of 50-100 °C. The surface root-mean-square (rms) roughness of the films reduced with increasing temperature at short-time annealing (up to 900 °C), while their surface morphologies were not changed. At the same time, the degradation appeared on the surface of the film with lower Al-content after 950 °C. Secondly, the Al0.43Ga0.57N film was annealed as long-time in the range of 1000-1200 °C in steps of 50 °C. The surface morphology and rms roughness of the film with increasing temperature up to 1150 °C did not significantly change. Above those temperatures, the surface morphology changed from step-flow to grain-like and the rms roughness significantly increased. © 2009 Elsevier Ltd. All rights reserved.