This chapter will cover most of the basic GaAs-related processing steps for GaAs field effect transistors, including most of the front end steps. Active steps are those that relate to the fabrication of the GaAs field effect transistor and do not include the interconnections or the integration of passive elements. FET fabrication and operation require an understanding of the GaAs semiconductor surface and its interface to metal junctions for etching, doping, contact formation and some particular aspects of performance optimisation.