We fabricated bottom gate thin-film-transistors (TFTs) with solution processed InGaZnO (IGZO) channel layers thermal-annealed at various temperatures. The solution based process inherently requires heat treatment at high temperatures to complete the chemical reaction of the thin films; therefore, thermal annealing is an important process to adjust the electrical characteristics of the thin films and TFTs. The IGZO channel layers retained structurally amorphous phase and high optical transparency at annealing temperatures of up to 600 degrees C. On the other hand, the electrical performances of the IGZO TFTs were highly sensitive to the annealing temperature. Thermal annealing at higher temperatures induced a negative shift of the threshold voltage (V(TH)) and an increase in the saturation mobility and on-off current ratio. The IGZO TFT annealed at 400 degrees C showed an appropriate V(TH) and on-off current ratio, but its saturation mobility was inadequate. Annealing at temperatures of more than 500 degrees C led to an excessive negative shift of V(TH), despite the high saturation mobility. (C) 2011 Elsevier B.V. All rights reserved.