We propose a new approach for calculating absolute surface energies of semipolar planes of AlN under metalorganic vapor phase epitaxy (MOVPE) growth conditions. The calculations using wedge-shape geometries demonstrate that the stable surface orientation depends on Al chemical potential. The calculated absolute surface energies of semipolar AlN(11 (2) over bar2) and (1 (1) over bar 01) are lower than that of N-polar AlN(000 (1) over bar) surface under Al-rich condition. On the other hand, the surface energy of N-polar AlN(000 (1) over bar) is lower than those semipolar surfaces under N-rich condition. The results on the orientation dependence of surface stability could provide valuable insights for the epitaxial growth conditions of AlN along semipolar orientations during the MOVPE growth.