Development of metal oxide semiconductors-based methane sensors with good response and low power consumption is one of the major challenges to realize the real-time monitoring of methane leakage. In this work, a self-assembled mulberry-like ZnO/SnO₂ hierarchical structure is constructed by a two-step hydrothermal method. The resultant sensor works at room temperature with excellent response of ~56.1% to 2000 ppm CH₄ at 55% relative humidity. It is found that the strain induced at the ZnO/SnO₂ interface greatly enhances the piezoelectric polarization on the ZnO surface and that the band bending results in the accumulation of chemically adsorbed O₂^- ions close to the interface, leading to significant improvement in the sensing performance of the methane gas sensor at room temperature.