Abstract: Semi-conductors, such as silicon wafers, are processed in two or more different reactors, e.g. reactors for the epitaxial growth of silicon, plasma etching, and/or vacuum metal deposition. The system is kept under constant vacuum. Common vacuum equipment, and a common gas distribution system, and a common silicon wafer loading chamber, are provided. A single reactor is maintained active at one time, while the dormant reactors are preferably kept under vacuum, and a control unit controls gas valves to selectively connect or disconnect each reactor to or from a source of treatment gas.