AlGaN/GaN HEMTs employing a tapered field plate, which decreases the gate leakage current and improves the breakdown voltage without any sacrifice of the forward electrical characteristics were proposed and fabricated. The tapered structure was fabricated by the wet etching process. The depletion region of the proposed structure expands toward the slope of the tapered field plate and the electric field concentration at the gate edge can be successfully suppressed. The gate leakage current of proposed device at VGS= -5 V and VDS= 100 V was decreased by 2-3 orders compared with that of the conventional one. The breakdown voltage of proposed device was 880 V while that of conventional one was 548 V.