A gas sensor including a first sensing component, a second sensing component and a voltage enhancement circuit is provided. The first sensing component is coupled between a first voltage and a first node, where an impedance value of the first sensing component is proportional to a gas concentration. The second sensing component is coupled between the first node and a second voltage, where an impedance value of the second sensing component is inversely proportional to the gas concentration. The voltage enhancement circuit is coupled to the first node to receive a node voltage provided by the first node, and correspondingly provides a gas sensing voltage.