Abstract: Evaluation arrangement for a thermal gas sensor with at least one heater and at least one detector. The evaluation arrangement is configured to obtain information about an amplitude of a detector signal of a first detector, and information about a first phase difference between a heater signal and the detector signal of the first detector. In addition, the evaluation arrangement is configured to form as an intermediate quantity, dependent on the information about the amplitudes of the detector signal and dependent on the information about the first phase difference, a combination signal, and to determine information about a gas concentration or information about a thermal diffusivity of a fluid on the basis of the combination signal.