We designed and fabricated AlGaN/GaN high-electron-mobility transistors (HEMTs) employing both a floating gate (FG) and a field plate (FP), which increase the breakdown voltage of AlGaN/GaN HEMTs significantly without sacrificing forward electric characteristics. The electric field strength at the gate–drain region of the proposed AlGaN/GaN HEMT was reduced successfully due to an increase in the number of depletion region edges. The breakdown voltage of the proposed AlGaN/GaN HEMT was 1106 V, while those of the conventional devices with only an FP or FG were 688 and 828 V, respectively. The leakage current of the proposed AlGaN/GaN HEMTs was 1.68 μA under a reverse bias of −100 V while those of the conventional devices with only an FP or FG were 3.21 and 1.91 μA, respectively, under the same condition. The forward electric characteristics of the proposed and conventional AlGaN/GaN HEMTs are similar. The maximum drain current of the proposed AlGaN/GaN HEMTs was 344 mA mm−1 while those of the conventional devices with only an FP or FG were 350 and 357 mA mm−1, respectively. The maximum transconductance of the proposed device was 102.9 mS mm−1, while those of the conventional devices were 97.8 and 101.9 mS mm−1. The breakdown voltage and the leakage current of the proposed device were improved considerably without sacrificing the forward electric characteristics. It should be noted that there were no additional processing steps and mask levels compared to the conventional FP process.