The performance of MOS circuits depends to a large extent upon the accuracy attainable in processing, that is, on technological and economic factors. Therefore it is important for a circuit designer to know the processing in sufficient detail that a reasonable compromise between different parameters may be reached. As the circuit designer must often be required to predict the manufacturing cost at a future time when the circuit may be in production, a rather detailed knowledge of manufacturing trends and limitations is required. In this chapter the processing of different transistors will be described whereas the next chapter will deal with the special considerations of integrated circuits.