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Trace level detection of H2S is of immense interest in diverse fields ranging from gas and oil exploration to dentistry. In the present work 0.12 μm thick sputtered SnO2 films, and a novel SnO2-CuO bilayer structure consisting of ultra thin (∼10 nm) CuO dotted islands (0.6 mm diameter) are investigated for H2S gas sensing. With the SnO2-CuO-dotted sensor, a high sensitivity of 7.3×103 at a low operating temperature of 150°C is obtained with a fast response time of 14 seconds for 20 ppm of H2S gas and a recovery time of 118 seconds under flowing air have been measured. The electronic and chemical interactions of the CuO catalyst layer on SnO2 in the presence of H2S have been analyzed in the light of space charge regions formed due to distributed p-type CuO islands on the n-type SnO2 thin film surface. Dissociated hydrogen available from the CuO-H2S interaction spills over and is found to be primarily responsible for the observed fast response characteristics.