TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - The etchant solution does not remove portions of the III-V semiconductor which do not have the conductive film pattern disposed on it. The III-V semiconductor comprises a compound selected from GaAs, InAs, InP, GaP, InGaAs, and InGaP. The III-V semiconductor comprises GaAs. The III-V semiconductor is doped. The conductive film comprises gold. The oxidizing agent comprises potassium permanganate (KMnO4). The acid is selected from sulfuric acid (H2SO4) and hydrofluoric acid (HF). The molar ratio of a concentration of the oxidizing agent to a concentration of the acid in the etchant solution is 10-2 to about 10-7. The method further involves varying a concentration of the oxidizing agent in the etchant solution. The method further involves: generating holes (h+) from the oxidizing agent on the conductive film pattern; diffusing the holes (h+) to a boundary of the conductive film pattern, III-V semiconductor, and etchant solution; and removing the holes (h+) from semiconductor substrate immediately upon the holes (h+) reaching the boundary. The method further involves forming features in the semiconductor substrate having a length-to-width aspect ratio of at least about 5:1, thereby forming an array of high aspect ratio semiconductor nanostructures. The array of high aspect ratio semiconductor nanostructures is an ordered array of nanowires. The semiconductor substrate comprises a first layer, a base substrate, and a second layer sandwiched between the first layer and the base substrate, where the first layer comprises a p-type or an n-type III-V semiconductor, the second layer comprises a SI-type III-V semiconductor, and the base substrate comprises a p-type or an n-type III-V semiconductor opposite to that of the first layer, and further where the selectively removing at least a portion of the III-V semiconductor includes selectively removing adjacent portions of the first and second layers and the base substrate to form a trench extending through the first and second layers and partially into the base substrate.