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Subject classification: 73.40.Qv; 85.30.Tv; S7.14 SiC devices have been the focus for several years as potential high voltage switches working at high temperature with very low on-resistance. Another competitive candidate for this application is the GaN HEMT (high electron mobility transistor). GaN has slightly wider bandgap, higher electric strength, and higher saturated velocity than SiC. The most prominent is that by utilizing the AlGaN/GaN heterojunction, the GaN HEMT has much higher charge density (up to 2 Â 10 13 cm --2 ) and mobility (up to 2200 cm 2 /Vs) in the channel compared to SiC MOSFET or JFET, yielding much lower on-resistance than SiC devices. GaN grown on SiC substrate also takes the advantage of high thermal conductivity of SiC. A GaN HEMT with a breakdown voltage of 1050 V was fabricated with a specific on-resistance of 3.4 mW cm 2 and current density of 4 kA cm --2 . State-of-art power device figure of merit of V 2 BR /R on = 3.24 Â 10 8 [V 2 W --1 cm --2 ] was achieved on this device. Projected performance of GaN HEMTs is also discussed and compared with SiC devices in this paper.