The significance of the surface states in isolated AlxGa1-xN/GaN hetero structures is investigated. A model based on a self-consistent solution of the Schrodinger, Poisson and charge balance equations is presented, The singular value decomposition is used to calculate the eigenstates of the real non-symmetric matrix which is obtained when a non-uniform mesh is used. The discontinuity of the spontaneous and piezoelectric polarization at the interface is taken into account. The results obtained for the 2DEG density and the surface potential agree well with theoretical and experimental data already published. (C) 2005 Elsevier Ltd. All rights reserved.