IGZO TFTs with various active-layer thicknesses were investigated. V-TH of TFT with 400 angstrom active-layer was -0.6V at R.T. and shifted 0.83 V at 230 degrees C while that of TFT with 700 angstrom active-layer was -1.2V and shifted 2.3V. We have investigated the effect of active-layer thickness on the IGZO TFTs.