1971, Joseph Stewart Bravman, Thermal effects in the operation of GaAs transferred electron microwave oscillators (page 138)
It was necessary to heatsink the device through the center conductor of the coax thereby producing a total thermal resistance from the active layer to the ambient of almost 50°C/watt.
2012, Robert B. Northrop, Analysis and Application of Analog Electronic Circuits to Biomedical Instrumentation (page 385)
The device itself can dissipate a peak power of 78 W when properly heatsinked and has a 65 W steady dissipation.