Zn@SnO₂ microspheres with hierarchical structure were prepared through a simple solvothermal method; the structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) showing the materials with extraordinary 3D nanoarchitectures. The gas sensing properties of the as-prepared pure SnO₂ and Zn-doped SnO₂ were tested toward various gases. The results showed that the SnO₂ sensor with 6.67 wt% Zn-doping displayed an excellent selectivity toward formaldehyde at the operating temperature 160 °C, which was considerably lower than most formaldehyde sensors in heater type among previous reports, in addition to giving a response of about 15.2 to 100 ppm, which is about 2.1 times higher than that of sensors based on pure SnO₂. The τ_res and the τ_rec values of the 6.67 wt% Zn-doped SnO₂ sensor to 100 ppm formaldehyde were 2 s and 2 s respectively, demonstrating extraordinary gas sensing properties, whereas those of the pure SnO₂ sensor were relatively long. The enhancement might be attributed to the unique morphology and increased oxygen vacancy due to the Zn doping.