A novel sensing material of NiO-doped SnO₂ polyhedra was prepared and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) spectroscopy and transmission electron microscopy (TEM). Gas sensing properties of the sensor fabricated from the as-prepared NiO-doped SnO₂ were systematically investigated and compared with those of pure SnO₂. The NiO-doped SnO₂ sensor exhibits a response of 6.7 to 30 ppm ethanol at 280 °C with the response and recovery times shorter than 0.6 and 10 s, respectively, which are much better than pure SnO₂. The enhanced sensing performances to ethanol are mainly attributed to the formation of p–n heterojunctions between p-type NiO and n-type SnO₂ and the increased alkalinity of SnO₂ by NiO doping.