We prepared indium zinc oxide (IZO) semiconductors for low temperature solution-processed thin-film transistors (TFTs). The sol-gel derived IZO films, annealed at 300 degrees C, are uniform and have smooth surface morphology (root-mean-square roughness of 0.27 nm). Both the composition and the film thickness need to be optimized for high performance TFTs. With the composition of In/Zn equal to 50/50 in mol percent, the IZO TFTs with a thickness of 10 nm exhibited the best performance for a clear switching behavior (on/off current ratio of 1.2x10(7)) and output characteristics (drain current of 3.7x10(-4) A), with a relatively high field-effect mobility (0.54 cm(2) V-1 s(-1)) and a low threshold voltage (1.9 V). The nonpassivated IZO-TFT stably operates over a two-month period without any significant change in the on/off current ratio and the mobility.