The damage introduced by CH4/H2 reactive ion etching (RIE) on Si-doped AlGaAs layers is studied by X-Ray Photoelectron Spectroscopy (XPS), Auger electron spectrocopy (AES) and electrical measurements on Schottky contacts. The XPS analysis of the surface stoichiometry after RIE exposure shows arsenic depletion and adsorbed carbon as the main characteristics. The carbon spectrum consists of a component due to atmospheric contamination and an additional photoelectron peak at 283 eV, which we correlate with the formation of Ga-C radicals at the AlGaAs surface during RIE. The reaction process at the Au/TiW/Ti/AlGaAs interface after RIE exposure and subsequent thermal annealing is monitored by AES. Also by this technique, carbon was detected at the Ti/AlGaAs interface and no interdiffusion was observed. The electrical behaviour of the contacts is characterized by capacitance-voltage (CV) and current-voltage (IV) measurements. Schottky barrier height, ideality factor and reverse breakdown were determined. The barrier height extracted from CV measurements of the samples exposed to RIE shows increased values (1.1 to 1.4 eV) compared to the reference samples (1.0 to 1.1 eV), depending on the aluminium concentration. The same behaviour was observed in the ideality factor. The results are explained by the formation of a p-n junction below the metal/AlGaAs barrier. Good agreement between experimental and theoretical values is found when the compensation of Si donors was taken into account.