In this study, we proposed a method to prepare GeO2 by treating porous Ge thin film with thermal annealing in O-2 ambient. After annealing, the morphological transformation from porous thin film to an island structure was observed. The crystallization and composition of the porous Ge thin film prepared using different annealing time in O-2, ambient were confirmed by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectra. Initial Ge composition was gradually oxidized to GeO2 with increasing annealing time. Comparing the photoluminescence (PL) results between Ge and GeO2, it was found that the visible photoluminescence originated from the germanium oxide. Photoluminescence measurements obtained at different temperatures exhibited a maximum integrated PL intensity at around 200 K. A possible explanation for this behavior might be the competition between radiative recombination and nonradiative hopping process. (C) 2007 Elsevier B.V. All rights reserved.