The etching behavior of AlxGa(1-x)InP(2) (0 <= x <= 1) in aqueous HCl was investigated for layers on their native GaAs substrates as well as for layers after releasing from their substrate and transferring to a foreign plastic carrier utilizing the epitaxial lift-off (ELO) technique. For InGaP2 layers on their native substrates the activation energy of the etching rate was determined to be 22 kcal/mol for HCl concentrations of both 6 and 12 M. The surface roughness of the partially etched AlxGa(1-x)InP(2) layers as determined with atomic force microscopy (AFM) was found to decrease with increasing aluminum fraction and to be smaller for 6 M than for 12 M HCl. AlxGa(1-x)InP(2) layers on foreign plastic carriers were often found to be not etched in HCl, in contrast to layers on substrates. This could not be attributed to a single cause and it is suggested that the nonetching behavior is related to a combination of factors, like exposure of the layers to the ELO process and strain induced by the foreign carrier. AFM studies showed an increased density of irregularities at the surfaces of the AlxGa(1-x)InP(2) samples that later showed nonetching behavior. (C) 2006 The Electrochemical Society.