A gas sensor having a heater layer; and a gas detector that is heated by the heater layer to detect a measurement target gas. The gas detector has a gas sensing layer, a diffusion layer that covers a surface of the gas sensing layer, and an absorption layer that covers a surface of the diffusion layer. The absorption layer has greater absorption of the measurement target gas than the diffusion layer, and the diffusion layer has greater diffusion of the measurement target gas than the absorption layer.