A dynamic thermal model is developed for a 350 A half bridge IGBT module and cooler which includes the effects of thermal cross-coupling between the various semiconductor elements. The parameters for the model are extracted from measurements of the transient thermal impedance from junction to ambient. A matrix representation of the model is developed which in turn is implemented into a working model in PSpice by use of a multi-term R-C network. Simulation results show that the cross-coupling effects during load power cycling are not negligible and are dependent on the load power frequency. It is concluded that typical thermal models derived from manufacturers' data may significantly underestimate junction temperature elevation in multi-device power modules.