NOVELTY - A method of metal assisted chemical etching involves: providing an electrically conductive film pattern disposed on a semiconductor substrate, where the semiconductor substrate comprises a III-V semiconductor; and selectively removing at least a portion of the III-V semiconductor immediately below the conductive film pattern by immersing the electrically conductive film pattern and the semiconductor substrate into an etchant solution comprising acid and an oxidizing agent having an oxidation potential less than an oxidation potential of hydrogen peroxide.    USE - As metal assisted chemical etching to form nanostructures (claimed); and for etching semiconducting materials. The nanostructures are used in many applications including solar cells, light emitting diodes (LEDs), laser diodes (LDs) such as distributed feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers, detectors, field effect transistors (FETs), thermoelectric devices, sensors such as along biological interfaces, and nanoscale processing units; and for forming electronic devices such as LEDs, solar cells, and Bragg reflector.    ADVANTAGE - The method allows effective production of high aspect ratio semiconductor nanostructures. The etching methods offer the potential to create high quality III-V photonic devices quickly and efficiently. The realization of high aspect ratio III-V nanostructure arrays by wet etching potentially transforms the fabrication of a variety of optoelectronic device structures including distributed Bragg reflector (DBR) and distributed feedback (DFB) semiconductor lasers, where the surface grating is currently fabricated by dry etching. Because it can occur at room temperature, MacEtch is not likely to introduce metal contamination, in contrast to bottom-up high-temperature metal-catalyzed nanowire growth techniques, and since MacEtch is a wet etch process, MacEtch avoids ion-induced surface damage typically seen in dry etch processes. This is crucial to III-V nanostructures for optoelectronic applications.