In this study, the effects of annealing temperature and thickness on zinc oxide formation in ZnO/glass thin film systems were investigated. For this purpose, ZnO thin films with thicknesses of 150-300 nm were obtained by thermal evaporation and then annealed in a range of 200-400 degrees C in air. The structural, optical, and electrical characterizations of ZnO/glass films were obtained. According to structural investigations, the deposited films contain Zn rich phases due to low oxygen content. By increasing the annealing temperature, the X-ray diffraction intensity of the Zn peaks that belongs to Zn rich phases is decreased and the ZnO phases were starting to form by oxidation at 300 degrees C. After 300 degrees C, polycrystalline ZnO phases are formed in all samples and at 400 degrees C, ZnO films become completely transparent. Scanning electron microscopy and atomic force microscopy analysis show that nanorods are formed on the surface of the ZnO films. It appears that these nanorods exhibit a random distribution and after annealing, columnar ZnO nanostructure growths occur more regularly. The electrical sheet resistances and resistivity analyses indicate that there is a transition from conductive Zn rich phases to semiconductor ZnO phases. This dramatic resistance increase is due to the transition from dark brown Zn rich phases to transparent ZnO phases. Moreover, the optical transmittance increases to up to 85% after annealing. Optical band gap values are calculated as 3.11-3.41 eV from UV-vis transmistance analysis.