ZnO nanowires are fabricated on p-type silicon substrates without using a catalyst. A simple horizontal doubletube system along with chemical vapor diffusion of the precursor, based on Fick's first law, is used to grow the ZnO nanowires. The substrates were placed in different temperature zones, and ZnO nanowires with different diameters were obtained. In addition to the nanowires, ZnO nanodiscs with different diameters were obtained on another substrate, which was placed at a lower temperature than the other substrates. The electrical property of the ZnO nanowires and nanodiscs are characterized by a simple DC circuit.