The contribution employs electrical simulation to assess the effect of the distribution of aluminium in the metal/GaN/AlGaN heterostructure on the leakage current. The heterostructure is characterized by a high density of traps causing an increase of the leakage current consisting of the thermionic emission component and of a non-negligible contribution of trap-assisted tunnelling. The leakage current is highly sensitive to the bending of the potential barrier E-c in the subsurface region of the GaN/AlGaN structure. The band bending is strongly affected by the sheet bound charge at the first GaN/AlGaNIGaN interface due to spontaneous and piezoelectric polarization. The overall charge depends on the concentration of Al, the distribution of Al at the first heterointerface having a strong effect on the formation of the potential barrier. (C) 2016 Elsevier B.V. All rights reserved.