Reflectance anisotropy spectroscopy (RAS) can be used to monitor (reactive) ion etching (RIE) of semiconductor samples. We present results on the influence of the Cl-2 content of the plasma gas on the RAS spectra during reactive ion etching. In a first step GaAs samples have been used and the RAS spectra are compared to results of secondary ion mass spectrometry (SIMS) on sample surfaces and depth profiles. In a second step a III-V semiconductor multilayer system has been investigated using the time-evolution of the average reflected intensity as an indication for the etch rate. In both cases usually even a high amount of Cl-2 does not disturb the surface-sensitivity of the RAS signal. (C) 2015 Elsevier B.V. All rights reserved.