Well-aligned ZnO nanorods arrays were fabricated by sintering powder Zn underneath a Si–SiO2 substrate. In this fabrication, ZnO was produced by the displacement reactions between Zn and SiO vapors. We found that these ZnO nanorods grew toward the  direction. The diameter and the alignment of these nanorods strongly depended on the sintering temperature. When the temperature was increased from 740 to 800 °C, the diameter of the rods was increased from 30–70 nm to 300–700 nm, and their alignment was also improved. A model is proposed to describe the formation of these nanorods.