Highly-uniform In₂O₃/CuO bilayer and multilayer porous thin films were successfully fabricated using self-assembled soft template and simple sputtering deposition technique. The sensor based on the In₂O₃/CuO bilayer porous thin film shows obviously improved sensing performance to ethanol at the lower working temperature, compared to single layer counterpart sensors. The response of In₂O₃/CuO bilayer sensors exhibit nearly 3 and 5 times higher than those of the single layer In₂O₃ and CuO porous film sensors over the same ethanol concentration, respectively. The sensing mechanism based on p-n hetero-junction, which contributed to the enhanced sensing performance was also experimentally confirmed by a control experiment which the SiO₂ insulation layer was inserted between the In₂O₃ and CuO layers to break the p-n junction. In addition, the sensing performance can be further enhanced by increasing the number of In₂O₃/CuO junction layers. The facile process can be easily extended to the fabrication of other semiconductor oxide gas sensors for practical sensing applications.