GaAs samples after wet chemical etching in nitric acid have been investigated for the first time by Raman spectroscopy. The GaAs surface prepared by this chemical etching results in a rough surface structure with an intrinsic chemically formed oxide film. The Raman scattering data suggest that the oxide layer is primarily composed of As2O3 in the crystalline form of arsenolite. This oxide film has been found to be subjected to a tensile stress. No experimental Raman observation of this kind of As2O3 arsenic oxide on oxided GaAs surfaces has been reported yet. No trace of amorphous arsenic and of elemental As has been detected.