The aim of this paper is to explain the intrinsic fail-safe capability of a high-voltage IGBT inverter source. The inverter is an imbricated cells structure which provides redundancy. The major failures can be either a wrong gate voltage (malfunctioning of the driver board, auxiliary power supply failure, dv/dt disturbance) or an intrinsic IGBT failure (over-voltage/avalanche stress, temperature overshoot). The IGBT failures are studied and show that no opening of the bondings can appear and consequently no risk of explosion. Owing to the imbricated cells structure, an IGBT failure can be withstand a few switching periods, with nevertheless non-optimized output waveforms. The design and the lab-test of a sensor able to perform monitoring and failure diagnosis are also presented. This real-time diagnosis allows either a safety stop or a remedial control strategy based on the reconfiguration of the control signals. The real-time reconfiguration allows to decrease internal stresses and to optimize the shape of the output voltage. In this case, a fail-safe operating may be gained for high power applications.