AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on Si on poly-SiC substrates formed by the Smart Cut (TM) process. The Smart Cut (TM) approach is an alternative solution to provide both a high resistivity and an excellent thermal conductivity template needed for power applications. Although the structure has not been optimized, devices with 0.7 mu m gate length show breakdown voltage of > 250 V, f(T) of 18 GHz, and f(max) of 65 GHz. (c) 2006 American Vacuum Society.