The selective dry etching between the AlGaAs and GaAs heterostructures is an essential issue for process controllability in heterojunction device fabrication. The mixture of CF4 and BCl3 has been recently proposed to replace the role of CCl2F2 used in AlGaAs/GaAs heterostructure etching process, where the nonvolatile AlF3 compound is formed to prevent the further etching in AlGaAs films. In this study, we systematically changed the mixing gas ratio between chlorine-base and florine-base gases, and investigated this influence on etching selectivity in AlGaAs and GaAs materials. Both CF4+BCl3 and CHF3+BCl3 gas mixtures were used, and the surface damage caused by the plasma bombardment in these two individual gas system was also included. Finally, we used these two characterized gas mixtures to etch away the n(+) GaAs layer in gate recess process for conventional GaAs MESFET fabrication. The result shows that CHF3+BCl3 gas mixture has demonstrated a lower surface damage, and was more suitable for the gate recess process.