Abstract: The present invention discloses a gas sensor made of field effect transistor based on ZnO nanowires (ZnO-FET) which operates according to the principle of metal-oxide-semiconductor field effect transistor (MOSFET) and has a charge carrier channel made of ZnO nanowires between source and drain. The gas sensor device disclosed in the present invention has three electrodes-gate, source and drain, so that it is different from the known gas sensor device which has only two electrodes-cathode and anode. The ZnO nanowires as charge channel in the gas sensor device of the present invention is an n-type semiconductor with high specific surface area, and its electric resistance can be controlled by the gate bias, so that the capability of the present device for sensing gas can be largely promoted.