Abstract: As the key device of power converter, the stability of insulated gate bipolar transistors (IGBT) can determine the reliability of the entire power converter to a certain extent. An IGBT module produced by a domestic company was broken down due to overvoltage stress failure in use, and some black dendrites were found in the unpacking module. The X-ray photoelectron spectrometer (XPS) was used to analyze the device failure. It was found that the black dendrites were composed of metal sulfides and sulfates. Through qualitative, quantitative and chemical state analysis of elements, some scientific guidances for the failure mechanism in the practical application of modules were provided. The possible sources of sulfur species pollution were analyzed in detail based on XPS data, while some improvements and prevention measures for device packaging materials and application environment were proposed.