The effects of oxidation temperatures on metal-oxide-semiconductor characteristics of sputtered zirconium thin films on germanium systematically investigated in an oxygen ambient. The samples were oxidized for 15 min at temperatures varying between 300 degrees C and 800 degrees C. The sample oxidized at 500 degrees C has demonstrated the highest electrical breakdown field of 16.6 MV cm(-1). The crystallinity of the film was evaluated by X-ray diffraction, Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopy analyses were also performed. The crystallite size and microstrain of the films were estimated by Williamson-Hall plot analysis. Optical microscopy was used to examine the sample surfaces and high-resolution transmission electron microscopy was carried out to investigate the cross-sectional structure. GeO2 was detected in samples oxidized at temperature above 600 degrees C. A possible thermal oxidation mechanism related to the diffusion of oxygen through the ZrO2 layer and formation of germanium dioxide has been proposed and discussed.