An extreme thin SiC buffer and Ga2O3 layer were deposited on silicon substrate sequentially with a r.f. magnetron sputtering system. Then the sample was annealed in the ambiance of ammonia at high temperature. Nanowires were found when the sample was tested with scanning electron microscopy (SEM). The composition of the nanowires is found to be GaN when the sample was tested with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). A nanowire was observed with transmission electron microscopy and it was even and uniform, with diameter of about 60nm. And the nanowire can be testified of wurtzite single crystal structure by electron diffraction (ED) analysis attached to the TEM. The high-resolution transmission electron microscopy (HRTEM) analysis to the nanowire indicates that the nanowire was single crystal with very good quality.