This document describes the thermal transient method to characterize the thermal resistance of an assembly consisting of a heat source (e.g. power device), an attachment material (e.g. solder) and a dielectric layer with electrode. It is suitable to determine the thermal resistance of materials and assembly methods as well as to optimize the thermal flux to a heat sink. Note: This method is not intended to measure and specify the value of the thermal resistance of a dielectric material. For that purpose, other standards exist. Examples are given in Annex A.