There is a growing demand for electronic signal processing at elevated temperatures. A number of approaches have been used to develop this capability. Silicon circuits could be developed and fabricated with an appropriate technology to cover increased temperature ranges. In a search for semiconductors with a wider energy gap to avoid leakage currents at high operating temperatures, one developed compound semiconductors such as GaAIAs on GaAs substrates. Efforts to use GaN are also useful, although difficult due to the lack of a suitable substrate material for lattice-matched epitaxial growth....