This article describes a complex measurement and simulation based characterization method of high current IGBT modules. The method begins with thermal transient tests aimed at the investigation of the thermal behavior of the module and the creation of a thermal map of the heat conduction path using structure functions. This information can later be used for different purposes, such as the calibration of a detailed thermal simulation model of the system or as a reference for later power cycling reliability tests. During this test the degradation of the die attach layer as a result of power cycles is tracked as it is indicated by the structure functions. In the article we demonstrate the steps of this method with a detailed case-study.