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H2S gas-sensing properties of a novel SnO2-CuO structure consisting of ultrathin (∼10 nm) CuO dotted islands (600 μm diameter) on 120-nm thick, sputtered SnO2 film are compared with a pure SnO2 and a SnO2-CuO bilayer sensor. The SnO2-CuO-dotted sensor exhibited a high sensitivity of 7.3×103 at a low operating temperature of 150°C. A fast response time of 14 s for 20 ppm of H2S gas and a recovery time of 118 s under flowing air have been measured. The electronic interaction due to modulation of the space charge regions between the distributed p-type CuO islands on the n-type SnO2 thin-film surface and the presence of adsorbed oxygen on the SnO2 support have been analyzed. Dissociated hydrogen available from the CuO-H2S interaction spills over and its chemical interaction with the adsorbed oxygen on the SnO2 surface is found to play a dominant role in the observed fast response characteristics.