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. Other work concerns electronic compo nent and circuit developments with SiC. Preliminary results have proved interesting. This book attempts to present the possibilities of such circuitry. Some of the solutions obtained so far are directly usable for the many applications where high environmental temperatures exist. Other concepts, particularly the more demanding ones, such as operation above 500 °C, still need much more researching. This also concerns estimates of device lifetimes for con tinuous high temperature operation. This book may help the potential user of such circuitry to find a suitable solution. It should also stimulate more research groups to enter this demanding effort. And finally, it should stimulate a broad awareness of the need and the solutions for this type of electronics. That is why Part One is devoted to high temperature applications.