Power MOSFET's may be used to obtain a low voltage drop in a rectifier circuit. This function will grow more important in future low voltage power supplies. In such a circuit, the MOSFET must operate in the “reverse mode,” in the sense that the current flow is opposite to the conventional direction. This paper discusses the I-V characteristics of power MOS transistors in the reverse mode by extending the theory for device operation in the normal mode. Three regions of operation in the reverse mode are identified. Calculated I–V curves compare favorably with the measured curves of a commercial power MOSFET.