Abstract We have fabricated indium–gallium–zinc (IGZO) thin film transistor (TFT) using SiOx interlayer modified aluminum oxide (AlOx) film as the gate insulator and investigated their electrical characteristics and bias voltage stress. Compared with IGZO-TFT with AlOx insulator, IGZO-TFT with AlOx/SiOx insulator shows superior performance and better bias stability. The saturation mobility increases from 5.6 cm2/V s to 7.8 cm2/V s, the threshold voltage downshifts from 9.5 V to 3.3 V, and the contact resistance reduces from 132 Ωcm to 91 Ωcm. The performance improvement is attributed to the following reasons: (1) the introduction of SiOx interlayer improves the insulator surface properties and leads to the high quality IGZO film and low trap density of IGZO/insulator interface. (2) The better interface between the channel and S/D electrodes is favorable to reduce the contact resistance of IGZO-TFT.