Medium-voltage (MV) high-power converters are usually realized using high-voltage semiconductors (3.3kV, 4.5kV or 6.5kV) operated with low-switching frequencies in the range of several hundred Hz and under hard-switching conditions. However, for medium-voltage high-power DC-DC converters employing transformer for galvanic isolation, it is attractive to increase switching frequency in order to reduce the transformer size. Therefore, it is usually required to consider the use of some sort of soft-switching method. Recently, DC-DC LLC resonant converters are gaining momentum, but are usually considered for low-voltage applications utilizing unipolar devices (MOSFETS). In this paper, switching properties of a medium-voltage bipolar semiconductor (6.5kV IGBT) are analyzed for a high-power LLC resonant converter. Experimental results are presented to illustrate the characteristic operating conditions, highlighting interactions between semiconductors and circuit properties, which both must be simultaneously considered, in order to achieve best utilization of a high-voltage semiconductor operating at higher switching frequencies.