Gas sensors based on organically hybridized SnO2 films are demonstrated. Upon exposure to CO gas, the electrical resistance of the hybrid sensor with amino groups in the organic components increases (R-increasing response), whereas other reducing gases such as H2 and CH4 gases cause the decreasing in the sensor resistance. For the n-type semiconductors like SnO2, the R-increasing response cannot be explained by the ordinary combustion mechanism. The appearance of the anomalous R-increasing response to CO gas can be controlled by the functional groups of the organic component. The hybrid sensor with hydroxy groups also exhibits the R-increasing response to CO gas, whereas it is not observed for the sensor with alkyl groups. The hybridization can improve gas selectivity of the SnO2 semiconducting gas sensors.