A new sensing mechanism of Si FET-based gas sensor using pre-bias

•A new capacitive-type FET (CFET) gas sensor based on Si FET is proposed.•Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material.•The NO2 gas-sensing characteristics are obtained by using pulse pre-bias method.•Depending on the polarity of pre-bias (Vpre), the CFET gas sensor exhibits the opposite ID behaviors.•The sensing mechanism is explained by using schematic energy band diagrams.