RF power levels of up to 40 mW atA dc to RF conversion efficiencies up to 4.5 % around 105 GHz have been demonstrated with GaAs TUNNE'rT diodes on integral heat sinks [1,2]. More than 90 % of the tested diodes have shown no saturation in RF output power or dc to RF conversion efficiency up to the highest applied bias current, which was chosen to ensure an operating junction temperature well below 250 Ã‚Â°C. Therefore, a significant boost in performance in these TUNNETT diodes can be expected by improving the heat dissipation. The MBE material designed for devices on an integral heat sink  and a selective etching technology originally developed for GaAs IMPA'rT diodes [3,4] were used in the first fabrication of W-band TUNNETT diodes on diamond heat sinks. The diodes were thermocompression bonded employing the same procedure as for GaAs W-band and D-band IMPATT diodes [3,4]. The standard open package on the diamond consists of four quartz standoffs and tapered leads. The diodes were tested in the same WR-10 waveguide cavity with a resonant cap as the diodes on integral heat sinks . The back short of the cavity was tuned for maximum RF power output.