In this paper a very high power density DC/DC converter module for automotive applications is investigated. The 14 V/42 V converter is specified to operate at a power level of 2.1 kW with a water cooled heatsink at 85/spl deg/C. The design and implementation of very high density passive components is discussed. Using the results of the passive component design, a prototype converter is built achieving a final power density of 170 W/in/sup 3/. The thermal performance of the passive components and converter module under different electrical and thermal excitations is investigated and recorded. Results are presented over the full excitation range.