The paper describes design and application of directly coupled inductor for interleaved GaN transistor based DC-DC converter with increased switching frequency. Low on state resistances and low switching losses of GaN transistors allows increase per-phase current ripple without significant increase in losses therefore application of directly coupled inductor becomes attractive. In the paper is given analysis of application of directly coupled inductor to achieve efficiency improvement and design considerations of such magnetic component. PSIM software and magnetic field simulation software based results are given and experimental tests are provided. Results shows that directly coupled inductor for high frequency converter could be used and could improve performance of the converter. Example of development of PCB winding based inductor is given in the paper.