A production process for protecting the surface of compound semiconductor wafers includes providing a multi-wafer epitaxial production system with a transfer and load module, a III-V growth chamber and an insulator chamber. The wafer is placed in the transfer and load module and the pressure is reduced to .ltoreq.10.sup.-10 Torr, after which the wafer is moved to the III-V growth chamber and layers of compound semiconductor material are epitaxially grown on the surface of the wafer. The wafer is then moved through the transfer and load module to the insulator chamber and an insulating cap layer is formed by thermally evaporating gallium oxide molecules from an effusion cell using an evaporation source in an oxide crucible, which oxide crucible does not form an eutectic alloy with the evaporation source