Promising cooling systems for high-power electronic elements are those based on vapor chambers and heat pipes which allow for the local heat flow to be dispersed from the electronic element to a larger surface area of the vapor chamber or the heat pipe. To reduce the thermal resistance of the cooling system, a finned radiator is installed on the outer surface of the vapor chamber or heat pipe. The authors propose a new design of the radiator which increases the heat transfer efficiency. The paper presents results of numerical simulation of heat transfer and aerodynamic resistance of the heat transfer surface with lamellar-split finning. The comparative analysis of heat transfer and aerodynamics was carried out for three types of radiators: with lamellar smooth finning, with lamellar split finning and with the sections of split finning rotated 30◦ against the air flow. It is shown that cutting the fins and rotating the split sections leads to an increase in heat transfer intensity and increase in aerodynamic resistance. The obtained results may be useful in the design of cooling systems for computer processors, power amplifiers for transmitting modules, energy-saving solid-state light sources, etc.