This study examined the influence of postdeposition annealing on the composition and local structures of amorphous In-Ga-Zn-O (IGZO) thin films using X-ray photoemission/absorption spectroscopy and X-ray diffraction. Upon annealing at high temperatures (>800 degrees C) in an N-2 environment, the Zn content in the a-IGZO films decreased significantly, suggesting ZnO volatilization. The resultant crystallization of the IGZO films was also observed. However, the bipyramidal local structures of Ga and Zn ions were still preserved, even after postdeposition annealing at 1000 degrees C, indicating the replacement of ZnO with GaO1.5 without altering the hexagonal In2Ga2ZnO7 crystal structure.