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An Al/sub 0.3/Ga/sub 0.7/N/GaN heterostructure field effect transistor (HFET) grown on semi-insulating SiC with an 0.2-/spl mu/m gate length is reported. A source-drain ohmic contact resistance of 0.15-/spl Omega/-mm was achieved through the use of high Al content and high n-type doping (1E19 cm/sup -3/) in the AlGaN donor layer and optimized metallization procedures. We obtained a maximum transconductance of 260 mS/mm, a saturated current density of 1.2 A/mm, and a maximum oscillation frequency in excess of 107 GHz in the devices. The results are one of the best achieved up to now, and they will open up the potential for the applications of AlGaN/GaN HFET's in high-power microwave radar, remote sensing, and communications.