A selective reactive ion etch process for GaAs high electron mobility transistor gate recess has been developed using BCl3/SF6 gas mixtures. The influence of gas flow ratio, pressure, and radio-frequency (rf) power on the selectivity was examined. An optimum selective etching process using a Plasma Therm 790 reactive ion etching system was determined to be 50 W rf power, gas flow ratio of BCl3/SF6 = 2.5 sccm/7.5 sccm, and chamber pressure of 50 mTorr. Excellent etch uniformity was achieved by using an HCl/ethanol solution to remove native oxide prior to plasma etching.