This investigation describes the synthesis and formation of the second phase of high-density arrays of vertically aligned ZnO:Ga nanowires on ZnO/glass substrates at 600 degrees C. As the concentration of the Ga is increased, the nanowire became shorter without any change in its diameter. The formation of the second phase, ZnGa2O4 (JCPDS no. 38-1240), was verified by X-ray diffraction and high-resolution lattice imagery, even though the concentration of the Ga was only 3.5 atom %. The formation of the second compound substantially influenced the physical properties of the nanowire.