To provide a heat sink having a heat transmission medium for enhancing the heat transmission capability of the heat sink.

A heat sink 10 has a plurality of fins 14 having cavities, a base 12 and a fluid heat transmission medium 16. The fin 14 is in thermal contact with the base 12 and is constituted so as to form a series of longitudinal flow path for passing air or the fluid medium. The fluid heat transmission medium 16 is contained in the respective cavities. The fluid heat transmission medium 16 intensifies the heat transmission capability of a heat sink 10 without enlarging the surface area, the size and/or the weight of the heat sink 10. When evaporated fluid heat transmission medium 16 condenses at the upper cooling wall of the fin 14, a large quantity of energy is transmitted from the evaporated fluid heat transmission medium 16 to the film 14. Thus, a larger quantity of the heat can be transmitted from the fluid heat transmission medium 16 to the fin 14, and then the fin 14 is able to diffuse the heat to the low-temperature surrounding part.