Abstract: A method and a device for measuring nitrogen oxides in a gas stream. A functional layer in the sensor senses nitrogen oxides and a measurable physical variable of the functional layer changes in direct correlation with the concentration of nitrogen oxide molecules in the gas. The functional layer is made of a material that, when heated to a specific operating temperature and held at that temperature, maintains an equilibrium between storage and desorption of the nitrogen oxide molecules, and this eliminates the need for a regeneration phase, as is the case with a dosimeter. At the specified operating temperature, the gas sensor indicates a direct relationship between the measured variable and the concentration of the surrounding gas.