The chemical etching characteristics of InGaP, GaAs, and InGaAsP in solutions of HCl, H2SO4, and H2O2 are investigated. With an appropriate solution composition, a mixture of two different selective etchants for InGaP and GaAs acts as a nonselective etchant for InGaP, GaAs, and InGaAsP, all lattice matched to GaAs substrates. The dependence of the vertical etching profile at the edge of etching masks and etching rate variation with solution aging are clarified, The variations of the etching rate and the etching profile are shown to be due to the dissociation of HCl and the formation of Cl-2 in the solution.