A gas sensor includes a substrate, a support layer, a base layer, a heater layer disposed on or above the base layer, a gas sensing layer that is disposed on or above one of the heater layer and the base layer and that has a gas concentration dependent electrical impedance, and a detection electrode that is electrically connected to the gas sensing layer and that detects the impedance of the gas sensing layer. The substrate has a cavity and an opening formed by the cavity. The support layer is disposed on the substrate so as to cover at least an entire periphery of the opening. The base layer is supported by the support layer above the cavity so as to be separated from the substrate. A portion of the support layer in contact with the cavity has a first phononic crystal structure structured by a plurality of regularly arranged through-holes.