We proposed the AlGaN/GaN high electron mobility transistors (HEMTs) employing the mesa field plate and carried out the detailed numerical simulation of device operation using ISE-TCAD. The reduction of peak electric field is required to achieve the high breakdown voltage of AlGaN/GaN HEMTs. Proposed AlGaN/GaN HEMT with both gate and mesa field plates simultaneously reduced the electric field concentration at the gate and the drain edge by decreasing the potential gradient along the 2-DEG channel. As the peak electric field at the drain edge was decreased, the breakdown voltage was increased by 66% compared with the AlGaN/GaN HEMT with the gate field plate only. The breakdown voltage could be increased without sacrificing any other forward characteristics due to the SiO2 passivation layer. (C) 2009 Elsevier Ltd. All rights reserved.