The performance potential of GaN FETs is substantially limited by device thermal requirements. Diamond is the highest thermal conductivity material, while GaN FETs on Si offer the best pathway for producing highly reliable AlGaN/GaN HEMTs. A novel technique has been developed to apply the diamond directly on top the AlGaN/GaN/AlGaN DH material structure.Two critical aspects of the wafering technique are the III-nitride etch and the interfaces. The III-nitride etch is a multi-step process. The III-nitride nucleation and transition layers, comprised of AlN and AlGaN, respectively, are etched with an ICP Cl2-based process. The etch effluent is monitored and when the process has reached the GaN buffer layer, it is manually terminated. The remaining GaN buffer layer is dry-etched with a proprietary process that has an exceptionally high selectivity between GaN and AlGaN (> 1,000:1). The sacrificial handle wafer bonding process is challenged by the roughness of the CVD diamond film. The CVD diamond coated 100 mm GaN-on-Si epiwafer has a matte gray appearance indicative of the very rough surface. The RMS roughness from AFM is 235 nm. This translates to a peak-to-valley height variation of as great as 2.5 μm. Poly-Si deposition then polishing is used to smooth the diamond surface. The poly-Si coated and polished CVD diamond wafer has a specular, shiny surface. The RMS roughness determined with AFM is 2.8 nm, or a reduction of ~ 84X over the original CVD diamond surface. This surface is adequate for bonding to the sacrificial handle wafer with a variety of processes. The most ideal process is a Si-Si fusion bond. High resolution STEM analysis of the material stack has been used to study the bulk material and interface quality. A key achievement of the program to date is the full-wafer AlGaN/GaN/AlGaN HEMT with PECVD SiNx transfer and selective etch. The selective etch control is indicated by the ability of the very thin AlGaN etch stop layer, ~ 10 monolayers thick, to inhibit the etch process. In this structure, with the CVD diamond included and ready for device fabrication, the 2DEG defining AlGaN barrier layer is decoupled from where the ohmic and Schottky contacts will reside. Because of this decoupling, there is no longer a necessity to compromise high-speed / high-frequency performance (e.g., through gate recess or epi structure design) and 2DEG characteristics. The material development aspects of this program will be presented along with the latest results from the epi-inverted N-polar GaN DH FET device fabrication and testing.