Abstract: Selective etching is an important step in GaAs process. As the wet-etching leads to undercut,poor selectivity and unrepeatable etching rate. It is necessary to research the dry etching. Although RIE and MERIE dry etching can be used for selective etching, they can cause serious damage, which affects the performance of devices and MMIC. ICP (inductive couple plasma) is a new method for low damage, high etching rate and high selective etching. In this paper, the selective etching of GaAs/AlGaAs is presented. The etching selectivity ratio of GaAs to AlGaAs is over 840:1.