We investigate a technique that has the potential to enhance the breakdown voltage (V-br) of AlGaN/GaN high electron mobility transistors (HEMTs) beyond 1 kV. The technique involves incorporation of a field plate (FP) connected to the gate and placed over a stepped insulator (SI). A comprehensive account of the critical geometrical and material variables controlling the field distribution under the FP is provided. A systematic procedure is given for designing a SIFP device, using 2-D simulation, to obtain the maximum V-br with minimum degradation in on-resistance and frequency response. Simulations show that, for a 2-DEG concentration of 1 x 10(13) cm(-2), the maximum V-br achievable with a stepped aluminum nitride (silicon nitride) insulator can be 2.6 (2.3) times higher than that with a uniform insulator; V-br similar to 1 kV can be obtained using a gate to drain separation as low as similar to7 mum. The methodology of this paper can be extended to the design of SIFP structures in other lateral FETs, such as MESFETs and LD-MOSFETs.