Iin-situ etching of GaAs and AlxGa1-xAs in LP-MOVPE has been studied using carbon tetrabromide (CBr4). This source is routinely used by us as a source for carbon doping in GaAs and AlGaAs. The etching rate decreases with increasing AsH3 partial pressure. While the etch rate is nearly constant for GaAs between 600 and 700 degrees C it strongly drops towards higher temperatures with higher Al content in the layers. A model based on blocking of the surface by non-volatile Al-Br compounds is proposed. The observed effects allow for selective in-situ etching of GaAs against AlGaAs. (C) 2008 Elsevier B.V. All rights reserved.