A dramatic increase in the GaAs etch rate has been observed with the addition of SF6 to BCl3 plasmas. The etch rate increases from 70 Angstrom/min in pure BCl3 to 4000 Angstrom/min with 70% SF6 in the total flow. Optical emission intensities of both molecular and atomic chlorine were observed to increase with SF6 addition, and the peak intensity of the atomic chlorine emission coincided with the peak in the etch rate. Argon was added to the mixture as an actinometer, and the argon emission intensity at 750 nm increased significantly with the addition of SF6. However, microwave measurements indicated that the average electron density decreases with increasing SF6 addition. It is believed that the increased production of etch species is due to an increase in the average electron temperature as a result of electron attachment heating.