We have developed highly sensitive, low-power gas sensors through the novel integration method of porous SnO2nanotubes (NTs) on a micro-electro-mechanical-systems (MEMS) platform. As a template material, ZnO nanowires (NWs) were directly synthesized on beam-shaped, suspended microheaters through an in situ localized hydrothermal reaction induced by local thermal energy around the Joule-heated area. Also, the liquid-phase deposition process enabled the formation of a porous SnO2thin film on the surface of ZnO NWs and simultaneous etching of the ZnO core, eventually to generate porous SnO2NTs. Because of the localized synthesis of SnO2NTs on the suspended microheater, very low power for the gas sensor operation (<6 mW) has been realized. Moreover, the sensing performance (e.g., sensitivity and response time) of synthesized SnO2NTs was dramatically enhanced compared to that of ZnO NWs. In addition, the sensing performance was further improved by forming SnO2–ZnO hybrid nanostructures due to the heterojunction effect.