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The fabrication and characterization of high performance AlGaN/GaN heterostructure field effect transistors (HFETs) grown on p-type SiC substrates are reported for the first time. The HFETs were fabricated with gate lengths of 0.25, 0.5, and 1 μm. These devices exhibited simultaneously high drain currents, high extrinsic transconductances, and excellent frequency response. The 0.25-μm gate-length devices produced a peak drain current of 1.43 A/mm, a transconductance of 229 mS/mm, a unity current-gain cutoff frequency of 53 GHz, and a maximum frequency of oscillation of 58 GHz. The unity current-gain cutoff frequency also exhibited little degradation as the drain-source bias was swept up to 20 V. These results represent a significant improvement over similar HFETs grown on sapphire substrates and are attributed to the higher thermal conductivity and reduced lattice mismatch associated with SiC substrates.