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Abstract The highly sensitive hydrogen sulfide (H 2 S) gas sensor was developed from a semiconductor composite structure composed of flower-like WO 3 microspheres whose surface was modified with CuO nanoparticles. The composites were prepared by a simple two-step hydrothermal method. The morphology and structure of the samples were examined by XRD, SEM, TEM and BET. The sensing properties of the samples on H 2 S at different operating temperatures were examined, and the performance of WO 3 /CuO with different molar ratios was also investigated. Gas-sensing tests show that WO 3 /CuO composites exhibit high response, excellent selectivity and fast response to ppm-level H 2 S at low operating temperature of 80 °C. Beyond that, WO 3 /CuO composites with 7:1 M ratio was responsive to 5 ppm H 2 S at room temperature (28 °C), and its sensitivity could be reached 16. In addition, the gas sensing mechanism of flower-like WO 3 microspheres modified with CuO nanoparticles was also thoroughly discussed. The enhanced sensing properties of composites were mainly attributed to the morphology structure and p-n heterojuction between flower-like WO 3 and CuO nanoparticles. Graphical abstract Image 1 Highlights • Flower-like WO 3 /CuO composite was synthesized by a facile two-step hydrothermal method. • Flower-like WO 3 /CuO composite microspheres could detect H 2 S gas at room temperature. • Highly sensitive and selective H 2 S gas sensor with fast response obtained at optimized low operating temperature (80 °C). • The gas sensing mechanism by the formation of p-n junction is thoroughly discussed in the manuscript. [ABSTRACT FROM AUTHOR]