The nonselective wet chemical etching of AlGaInP and GaAs in pure iodic(HIO3)acid and in hydrochloric acid (HCl) associated different oxidant agents has been evaluated. The pure iodic acid is nonselective between III–V phosphides and arsenides. Unfortunately, the etch of GaAs results in a very rough morphology and an etch rate 10 times greater than on AlGaInP. The mixing of HCl with different oxidants such asH2O2gives a nonselective etchant. HoweverH2O2dissociates HC1 to form chlorine which produces a wide evolution of the etch rate with time incompatible with the reproducibility necessary for device technology. This phenomenon is easily explained and solved using oxidant agents such asKIO3, K2Cr2O7.Added to HCl, they give chemically stable solutions but unfortunately they give rise to a strong undercut of the AlGaInP under the GaAs. The iodic acid is also a strong oxidant. Therefore a diluted solution of(HCl, HIO3, H2O)is proposed which gives an evolution of the etch rate between 300 and 3000 Å/min with water dilution, a good stability in the time, and similar etch rates on the two materials with very good morphologies. Applied to heterostructure no undercut of the AlGaInP is observed.