We fabricated a 0.5-μm-gate MESFET on a bulk 4H-SiC semi-insulating substrate using ion implantation for the channel and contact regions. Our device design used a thin, highly doped channel layer, which was implanted at single energy to improve the device’s RF characteristics. The electrical characteristics of the ion-implanted MESFET annealed at 1700°C were better than those of the ion-implanted MESFET annealed at 1300°C. The fabricated ion-implanted MESFET has a maximum transconductance of 32.8 mS/mm and an fT/fmax of 9.1/26.2 GHz. The saturated output power was 26.2 dBm (2.1 W/mm) at 2 GHz. These values were the same as those of the conventional epitaxial MESFET with a recessed gate.