The original influence of water on the back-channel of sol-gel derived amorphous indium-gallium-zinc-oxide thin film transistors was studied in various relative humidity environments. As humidity increased from 0 to 80%, the mobility increased from 0.22 to 0.24 cm(2)/(V s), threshold voltage decreased from 6.6 to 4.4 V, and subthreshold swing changed from 0.77 to 1.27 V/dec. The conflicting phenomenon among the three parameters was suggested to be due to a division of the gate voltage by the water molecules which adsorbed on the thin film transistor back-channel and acted as dipoles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3526097] All rights reserved.