The impressive features, both in a design and technical aspect, of the Organic LED (OLED) lighting technology have attracted the interest of the research and commercial world and have recently be in the spotlight of the automotive industries, like the Lighting Department of Audi. Some of the most exciting features of these lights are the exibility, transparency and the very small thickness. It is reasonable, therefore, that in order to take full advantage of this new technology the electronics that drive these lights, that is the dc/dc converter, should also be characterised of low prole, exibility and small size. A boost towards the direction of the converter minimization and high power density operation could be the recently commercialised power switching technology of Gallium Nitride (GaN) devices. This technology, which exploits the advantages of the wide band gap semiconductors, offers high frequency, high power density, low switching losses operation and low profle design, as well. As every newly commercialised technology, the areas of application that at most exploit the advantages of these switches are still to be found, but it is expected that applications that require high power density or low profle features, like the OLED applications, could benefit the most from the GaN technology. This area is the exact topic of the current master thesis. At this project a dc/dc converter based on GaN switching devices is designed and built. The converter is purposed for the driving of Organic LED lights that belong to the tail light system of a vehicle. As such, the electrical, mechanical and thermal specifications of the converter are based on the guidelines of the Lighting Department of the Audi automotive industry and the nature of the Organic LED lighting. At this thesis, the required dc/dc converter is designed, built, measured and assessed for its adequacy to the defined requirements. During the design part of this project the necessary simulations are conducted. For the purpose of estimating the losses of the GaN device a detailed analytical model for the switching transients is used. Also, both the possibilities of using a planar and a discrete coil are investigated during the simulations and the two components, which were built in the lab, are compared experimentally. A final prototype of the converter is also built in the lab and the experimental and simulated results are then compared and assessed. The assessment of the results showed that the features of the GaN device can be fully exploited at this application and can offer the low profile and high power density requirements. In order, however, to achieve the minimization of the magnetic component more advanced and wider range of core materials are required, especially if a planar coil is desired. Finally, full exploitation of the detailed analytical GaN loss model requires specialised software tools or accurate analytical models in order to determine the values of the various parasitics and the thermal resistance of the component, both strongly related to the PCB layout. This, also, means that during the design procedure in order to achieve better accuracy -which is required at applications which push the frequency to the limits - the PCB design layout parameters should be included in the iterative process of the parameter specification