It has been seen in this chapter that the GaAs field effect transistor is playing an important role in the development of integrated circuits. Analogue microwave circuits fabricated on gallium arsenide have a performance which is unattainable using silicon. Digital logic circuits on GaAs have a five times speed advantage over silicon at the present time but the massive investment in the very high speed IC (VHSIC) program in the USA will undoubtedly narrow the gap. However, there are many promising logic architectures based on GaAs MESFETs, JFETs and MOSFETs which will progress rapidly as the technology matures. The bibliography below is intended as a guide to further reading and papers not referred to in the text are also included. The complexity of both analogue and digital GaAs Ics is increasing rapidly. Markets for GaAs Ics are becoming well defined and a $1500 million market in the USA alone is anticipated by 1990, which assuming modest requirements in the early 1980's infers a growth in the market in excess of 100% per annum over the next decade.