Abstract: Wet chemical etching techniques for etching via holes through GaAs substrates were comparied with an inductively coupled plasma （ICP） dry etching process. The latter was developed to etch via holes through GaAs substrates by using CCl₂F₂/Ar gas mixtures. By optimizing the pressure, RF power, CCl₂F₂/Ar ratio, a smooth via profile and a maximum etching rate （4.3txm/min） are achieved at 43Pa with CCl₂F₂ of 200seem, Ar of 10sccm, source power of 400W, bias power of 14W and self-bias of 120V.