The　wet　oxidation　of　AlGaAs　with　high　Al　content　in　a　distributed　Bragg　reflectors　(DBR)　is　studied　by　scanning　electron　microscopy　(SEM)　and　transmission　electron　microscopy　(TEM).　Some　voids　distribute　along　the　oxide/GaAs　interfaces　due　to　the　stress　induced　by　the　wet　oxidation　of　the　AlGaAs　layers.　These　voids　decrease　the　shrinkage　of　the　Al2O3　layers　to　8%　instead　of　the　theoretical　20%　when　compared　to　the　unoxidized　AlGaAs　layers.　With　the　extension　of　oxidation　time,　the　reactants　are　more　completely　transported　to　the　front　interface　and　the　products　are　more　completely　transported　out　along　the　porous　interfaces.　As　a　result,　the　oxide　quality　is　better.