Controlled anodic oxidation far achieving a better control of etch depth in AlGaAs semiconductor structures is studied. The rates of material consumption and oxide thickness growth for p(++)-GaAs and p-Al(0.38)G(0.62)As are given for the citric acid/glycol/water electrolyte. The etch profiles for GaAs/Al0.45Ga0.65As and GaAs/Al0.60Ga0.40As layer sequences in laser diode structures are presented. The underetch is rather high and depends on oxidation conditions (constant voltage or constant current). The profile obtained is very rough for constant voltage oxidation and much better when using constant current conditions. The latter also improves the uniformity of oxide growth. The etch rate of the anodic oxide in diluted HCl is much larger for GaAs than for AlGaAs.