Efforts to minimize the size and material usage of power converters are reflected in efforts to increase the switching frequency. The problem is that semiconductor switching losses are proportional to the switching frequency, so it is necessary to find ways to keep efficiency high at higher switching frequencies. GaN transistors have made it possible to improve the parameters of many topologies due to a better figure of merit (FOM) ratio between the value of parasitic capacitances and drain to source resistance. Thanks to GaN technology, it is possible to increase the soft switching range in the inverter of PSFB converter and thus reduce switching losses. This paper addresses the selection of semiconductor transistors for a synchronous rectifier operating at 500 kHz. Based on mathematical calculations and simulation results in the program PLECS, the converter was designed and measured under laboratory conditions. The paper highlights the advantages and challenges of using GaN transistors in synchronous rectifiers, which, when properly applied, enable lower losses and thus higher efficiency at a switching frequency of 500 kHz.