High density plasma etching of III-V compound semiconductors is critically important to the development of advanced optoelectronic and high frequency devices. Unfortunately, the surface chemistry of these processes is not well understood. In an effort to monitor surface processes and their dependence on process conditions in a realistic etching environment, we have applied mass spectroscopic techniques for the study of GaAs etching in Cl2/Ar chemistry. Etch product chlorides were monitored, together with optical measurement of the surface temperature by diffuse reflectance spectroscopy, as pressure (neutral flux), microwave power (ion flux) and rf bias of the substrate (ion energy) were varied. Observations from the spectroscopic techniques were correlated with ex situ surface damage assessments of unpassivated surfaces by photoreflectance spectroscopy. As a result, insights are made into regions of process conditions that are well suited to anisotropic, low damage etching.