Type 5VAx family of structures are fabricated by ACST planar process on thinned s.i. GaAs substrate. Air-bridge interconnected mesas provide for a low parasitic capacitance and are fully passivated against harsh environment. The 5VAx structure represents three in series connected anodes, optimised for operation in varactor mode. The ACST Varactor Process provides nearly-ideal electrical characteristics, which allow for low losses (high efficiency) and high power-handling capability.