We report on the ac and reverse recovery behavior of organic pentacene/ZnO thin-film diodes fabricated on plastic substrate. The 50 nm thin pentacene was evaporated on 60 nm thin ZnO that was deposited by atomic layer deposition at 100 degrees C. Our thin-film diode showed a much faster reverse recovery (similar to 70 ns) compared to that (similar to 5 mu s) of the Si control diode, although it also reveals a lower forward current of similar to 3 mA at 2.5 V than that of the Si control (10 mA at 0.6 V). It is because our thin-film diode has little influence of the minority carrier unlike the Si control diode. We thus conclude that the pentacene/ZnO thin-film diode is promising as a fast switching device. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3428743] All rights reserved.