In this paper we have investigated the effectiveness of employing the Single Field-Plate (SFP) technique to enhance the breakdown voltage (BV) of AlGaN/GaN power High Electron Mobility Transistors (HEMTs).A systematic procedure is provided for designing the SFP device, using two dimensional(2-D) simulation to obtain the maximum improvement in the drain-source current (IDS) and to achieve maximum breakdown voltage.It is found that significantly higher breakdown voltages can be achieved by just raising the thickness of the passivation layer Si3N4 beneath SFPand raising SFP length(Lsfp) between the source and drain.We demonstrate that when a single field-plate connected to the source is employed,both breakdown voltage and IDS can be enhanced by optimizing the passivation layer Si3N4 thickness beneath the SFP as well as the SFP geometry