Ga-doped and undoped SnO2 porous microflowers (SPMs) were synthesized by a facile hydrothermal method. The presence of Ga in the SPMs and their structure was determined by X-ray powder diffraction (XRD), energy-dispersive spectroscopy (EDS), X-ray photoelectric spectroscopy (XPS) and scanning electron microscopy (SEM). Compared with the pure SPM sensor, the 3 wt% Ga-doped SPM sensor exhibits a lower detection limit (3.0/ 0.1 ppm) and improved sensitivity (95.8/50 ppm) to formaldehyde at 230 degrees C, which is 4.5 times greater than the pure SPM sensor (21.2/50 ppm). Furthermore, the Ga-doped sensor shows a short response-recovery time (3/ 39 s) and good selectivity for formaldehyde.