A challenge for low-valence cation doping in SnO2 materials is that the sharply elevated baseline resistance is detrimental to sensor stability and the subsequent signal acquisition. In contrast, Homovalent doping has little effect on resistance but the effective homovalent dopant is few. Herein, we find the non-metallic element Se is prone to form cationic SeSn defects in SnO2, which can improve the sensitivity of the SnO2-based sensors with a moderate rise in baseline resistance. The homovalent Se doping make the species and ratio of adsorbed oxygen on Se-doped SnO2 surface basically unchanged after doping. Further experiments and theoretical calculations confirm the sensitization mechanism of Se-doped SnO2 can be attributed to the higher activity of adsorbed oxygen on its surface. Therefore, the sensor based on Se-doped SnO2 can have sufficient sensing-reactions and charge transfer at a temperature close to the maximum value of the baseline resistance, which makes the sensor better to sensitize the target gases requiring high temperature for sensing-reactions. This noble metal-like activation behavior of Se dopant is derived from the easier breaking of Se-O bond compared to Sn-O bond during CO oxidation which provides a new basis for the selection of dopants from the perspective of bond energy.