Creation of nanoscale building blocks with various sizes and shapes are critical for the progress of nanotechnology. The synthesis of GaN nanowires by chemical vapor deposition (CVD) using Ga and NH3 as source materials on SiO2/Si substrate was systematically studied. Various types of catalyst materials, including gold (film and nanoparticle), nickel (film and nanoparticle), silver, cobalt and iron, have been used. The growth runs have been carried out at temperatures between 800 and 1100oC under two different carrier gases; H2 and Ar. Initial growth runs using Ar as carrier gas resulted in microscale-faceted nanostructures and short nanorods regardless of the growth temperature or reactor pressure. We have successfully achieved ultra-dense interwoven long nanowires using hydrogen as carrier gas at 1100oC. In fact, the yield has been very high for both gold and nickel catalysts. It should be emphasized that combination of high-temperature and hydrogen has resulted in ultra-dense interwoven long GaN nanowires. These results suggest a radical change in growth kinetics at high temperatures in the presence of H2. The GaN nanowire diameters are in the range of 15 nm to 50 nm and lengths up to hundred microns. The grown nanowires have been characterized by scanning electron microscopy (SEM with EDS), atomic force microscopy (AFM), x-ray diffraction (XRD), and transmission electron microscopy (TEM).