Developments in the etching process for fabrication of back-side via holes in GaAs based monolithic microwave integrated circuits are reviewed. Attention is focused on critical issues concerning via hole fabrication. The requirements of the process of via hole etching are considered. The suitability of various fabrication techniques, and the associated chemistry, has been examined. The effects of various process parameters such as power, pressure, and gas flow rate on the etch characteristics have been discussed. The influence of the masking material, via hole dimensions and the wafer size on the etch characteristics have been discussed from the point of view of increasing packing density in advanced chip fabrication. Finally, the state of the art and the issues concerning the via hole etching process are described.