A gas sensor system includes a gas sensor capable of producing an output signal responsive to the concentration of a specific gas component in measurement gas, a gas concentration determination device that makes electrical connections to the gas sensor and determines the concentration of the specific gas component according to the output signal of the gas sensor, a failure detection device that detects a potential failure in any one of the electrical connections, a sensor temperature determination device that judges whether the gas sensor has been cooled to a predetermined temperature or lower with reference to a sensor temperature parameter and a failure identification device that, when the gas sensor has been cooled to the predetermined temperature or lower, outputs a diagnosis signal to the gas sensor, measures potentials of the electrical connections under the diagnosis signal and identifies in which of the electrical connections the potential failure is occurring based on the measured potentials.