Citric acid/hydrogen peroxide (C6H8O7:H2O2) at volume ratios from 0.2:1 to 20:1 was found to provide selective etching between GaAs1-xSbx (x=0.15 to 1.0), Al0.5Ga0.5Sb, InAs, and various III-V semiconductor materials for use in new GaAs and InP based heterostructure transistors and optoelectronic devices. By choosing different concentration volume ratios of citric acid to hydrogen peroxide (chi C6H8O7:1H(2)O(2)), highly selective as well as uniform (nonselective) etching regions were found to exist in these material systems. Etchant selectivities greater than 50 were found for most combinations of the III-V semiconductor materials under investigation, with selectivities of over 100 measured for GaAs/GaSb and InAs/GaSb material combinations, and with selectivities of over 3850 calculated for InAs/Al0.5Ga0.5Sb to 13,650 for GaAs/Al0.5Ga0.5Sb. The highest overall etch rates were measured for InAs and the lowest etch rates were found for Al0.5Ga0.5Sb. The etch rate for the GaAs1-xSbx materials systematically decreased from the highest etch rate for the smallest Sb mole fraction examined of GaAs0.85Sb0.15 to the lowest etch rate for GaSb. The dramatic change in etch rate with citric acid/hydrogen peroxide volume ratio previously observed for the GaAs/AlGaAs material system was also observed for GaAs0.85Sb0.15, but this effect was not seen in higher Sb mole fraction alloys of GaAs1-xSbx examined. Al0.5Ga0.5Sb and GaSb were found to have very low etch rates with this etchant system at all volume ratios, making both materials suitable as an etch stop layer for simplified processing in device fabrication. Finally, citric acid/hydrogen peroxide can be used to preferentially etch these materials through a photoresist mask, since it does not erode photoresist at any volume ratio.