The gate forward leakage current in AlGaN/GaN High Electron Mobility Transistors (HEMTs) is investigated. It is known that the gate forward leakage current reduces as effective electron barrier height (q phi(b)) grows. Therefore, an energy-band modulation (EBM) technology using fluorine-plasma treatment or P-type doping is presented to introduce the negative fixed charges into AlGaN layer. The introduced negative fixed charges can modulate the conduction-band profile in AlGaN layer, resulting in higher effective electron barrier. An analytical model is proposed to illustrate the conduction-band profile. It is suggested that as introduced negative fixed charge concentration exceeds a critical value, an additional electron barrier (q Delta phi(b)) is achieved, contributing to reducing the gate forward leakage current. Based on this theory, the fluorine-plasma treatment is implemented to carry out EBM technology in this work. Experimental results confirm that the additional electron barrier q Delta phi(b) of 03 eV is obtained for the fluorine-plasma treatment condition of 60W and 120 s. Thus, the gate forward leakage current is decreased by one order magnitude lower than that of HEMT device without fluorine-plasma treatment. The analytical results are in good agreement with numerical simulation and experiment results. (C) 2012 Elsevier Ltd. All rights reserved.