In this work, we have studied the characterizations of SnO2 thin films deposited on Si substrates. The SnO2 thin films were polycrystalline and produced by using vacuum-evaporation with a two-step process : evaporation of tin metal films and then oxidation of these metal films. Surface morphology of the SnO2 thin films was observed by atomic force microscopy (AFM). It was found that the grain size acquired in AFM images correlates with the oxidation temperature and the oxidation time. The kinetics of the grain growth is suggested to be a three-dimensional diffusion limited process. The diode current-voltage (I-V) characteristic of the SnO2/Si heterojunctions (isotype and anisotype) was measured in the temperature range of 14-383 K. Changes in the diode ideality factor and threshold voltage with temperature are discussed.