In nanotube-based electronics, Al2O3 nanotubes will play a very important role. A method is reported that yields nanotubes with controllable, uniform wall thickness. The Figure represents the stage of the synthesis in which ZnO nanowires synthesized on a thick polycrystalline ZnO layer on a Si substrate have been coated with Al2O3 and the ZnO partially etched away. When the etching is complete, Al2O3 nanotubes remain.