A gas sensor includes a piezoelectric substrate; a resonator in an electrode region on an upper surface of the piezoelectric substrate, the resonator including interdigital transducer (IDT) electrodes and IDT pads connected to the IDT electrodes, the IDT electrodes configured to generate a surface acoustic wave in a center region of the electrode region, the surface acoustic wave propagating in a first horizontal direction; a sensing film in the center region of the electrode region on the upper surface of the piezoelectric substrate, the sensing film including a sensing material that interacts with a target gas; and a heater in an edge region surrounding the electrode region on the upper surface of the piezoelectric substrate, the heater including heater electrodes configured to heat the sensing film and heater pads connected to the heater electrodes, the heater electrodes and the heater pads forming a closed conduction loop.