The group III-nitride material system has been demonstrated by many groups to produce high performance, heterostructure field effect transistors (HFETs). AlGaN/GaN heterostructures yield high two-dimensional electron gas densities with high carrier mobilities and simultaneous high breakdown field. Devices based on this structure perform well at high power and at high frequency operating conditions. Most AlGaN/GaN HFETs to date have been produced on sapphire or silicon carbide substrates due to the limited availability of bulk GaN substrates. There are limitations in using these substrate materials in either thermal conductivity, cost or wafer diameter. The use of silicon substrates can overcome the issues of sapphire and SiC that limit manufacturability. In this work, results from HFETs fabricated on 100-mm silicon substrates using a proprietary MOCVD reactor design will be presented. The quality and uniformity of the GaN epitaxy, the microwave characterization of these devices at 2 GHz, and the thermal performance of large periphery devices on this material will be detailed. The electrical performance of these devices is found to be comparable to that of early devices on sapphire and SiC. The results will illustrate the viability of silicon as a low cost, manufacturable platform for AlGaN based devices from the standpoint of epitaxy, device performance, and thermal power handling. (C) 2002 Published by Elsevier Science Ltd.