The paper is devoted to determination of the efficiency of hybrid micro modules of power inverters with a switching frequency in the range from 0.1 to 0.3 MHz. To carry out the research SiC transistors C3M0065090J and eGaN EPC2035 transistors have been chosen, as these transistors have small cases and good frequency properties. Hybrid micro modules of power inverters were created on the basis of selected transistors using a welding device of one-sided contact micro welding. The test bench makes it possible to investigate the hybrid power micro modules under various operating conditions and cooling methods. The module efficiency research results are presented, when direct liquid cooling by silicone oil was used and the switching frequency was changed. It is established that the efficiency of the hybrid power micro modules exceeds 0.9, even when the switching frequency equals 300 kHz, if eGaN transistors EPC2035 are used in the module.