A method for determining a temperature of a measurement sensor for determining an oxygen concentration in gas mixtures. In particular, the measurement sensor may be used in exhaust gases of internal combustion engines. A detection voltage which corresponds to the oxygen concentration and is provided by a Nernst measuring cell is evaluated, and the measurement sensor is regulated to an operating temperature using a heating device. The internal resistance of the Nernst measuring cell is determined in a first temperature range and is used to infer the temperature of the Nernst measuring cell, and the internal resistance of the heating device is determined in a second temperature range and is used to infer the temperature of the Nernst measuring cell.