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The marriage of traditional gas-sensing semiconductors with low dimensional nanostructures is expected to exhibit interesting properties in the detection of hazardous gases. Herein, novel hollow-spherical heterojunctions are assembled for thin film gas sensors by using p-type black phosphorus (BP) and n-type tin oxide (SnO 2). Green synthesis strategies are employed to prepare BP nanodots and SnO 2 quantum dots. The aerosol-assisted chemical vapor deposition is used to prepare thin films with hollow-spherical heterojunctions. The BP incorporation significantly improves the gas-sensing properties of SnO 2 -based thin films, which demonstrate excellent response and repeatability to H 2 S at room temperature. The BP-SnO 2 heterojunction demonstrates more than twice the response and sensitivity of pristine SnO 2 thin film. Moreover, the recovery ability is significantly improved and LOD is decreased to 50 ppb. The hollow-spherical heterojunction has a joint gas-sensing mechanism contributed by both of SnO 2 and BP. The SnO 2 provides fundamental receptor function for gas detection while incorporated BP facilitates the adsorption of target H 2 S and provides additional electrons through the p-n junction tunnel. In addition, a slight negative dependence on humidity is observed for the gas sensor. It is ascribed to the competitive adsorption of water molecules on the BP-SnO 2 heterojunction surface against H 2 S molecules and chemisorbed oxygen. This work not only proposes novel heterojunction nanostructures for room-temperature gas detection, but also contributes to the functional integration of traditional gas-sensitive materials and emerging 2D materials in sensor technology. [ABSTRACT FROM AUTHOR]