In this study, gallium nitride (GaN) nanowire (NW) arrays were grown on a gold-coated Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). The important parameter that decides the density of GaN NWs was considered to be growth temperature. Therefore, in order to study the effect of growth temperature, we grew GaN NWs at various growth temperatures, namely, 800, 850, 900, 950, and 1000 °C, under identical growth conditions. The optimum growth temperature was observed to be 950 °C, and the diameters of the grown GaN NWs were in the range from 80 to 250 nm, and the average length was 3 μm. The surface morphology and optical characterization of the grown GaN NWs were studied by field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and cathodoluminescence (CL), respectively. Energy dispersive X-ray spectroscopy (EDX) analysis confirmed the presence of gallium and nitrogen in the grown NWs. The PL and CL spectra revealed sharp peaks at 366nm with a full width at half maximum (FWHM) of 102meV and at 3.36 eV with a FWHM of 85 meV, respectively, indicating that the grown GaN NWs were highly crystalline. © 2009 The Japan Society of Applied Physics.