Structural, optical, chemical and electrical properties of thin films of ZnO obtained by spray pyrolysis over Pt or silica substrates are determined at temperature ranges between 223 and 373 K. The thin films are pure ZnO with a preferred crystalline orientation of (0 0 2). Grain-boundary barriers are created by the band bending and the mobility of charge carriers is limited by the thermal field emission of electrons at the grain-boundary barriers. The density of ionized acceptor atoms and the width of the space charge, both obtained from the capacitance-voltage (C-V) method, are consistent with the theory of the depletion layer in the Schottky barrier device. The density of states of defect, obtained from admittance spectroscopy, only presents a maximum at approximately 0.44 eV, whose position in the band gap does not change under bias.