Cooling systems significantly contribute to the total mass and/or volume of power electronic systems especially for aerospace application where it will directly increase the operating cost of the aircraft. This paper investigates the heat sink parameters that contribute to the thermal resistance as well to weight of the high power density converter. The lowest heat sink thermal resistance for any type of coolant can be achieved by choosing a greater number of flow channels and thicker fin thickness. To minimize the weight, lower number of channels and thinner fins are desirable. The design case of 50kW power converter with 1.16% power loss using the most promising coolant in aircraft application is investigated and presented. Manufacturing constrains of the heat sink have also been taken into account.