To provide a heat sink which mounts a semiconductor element used for a laser for optical communication, etc., and dissipates the heat generated from the element.

A heat sink 1 used for mounting a semiconductor element 5 and dissipating the heat generated from the element 5 is composed of a composite material of Al-group carbon fibers and the heat sink mounting surface 4 of the heat sink 1 has a coefficient of thermal conductivity of ≥200 W/m.k in the planar direction and a coefficient of thermal expansion between 4×10-6/°C and 10×10-6/°C. Therefore, the coefficient of thermal conductivity and coefficient of thermal expansion of the heat sink 1 become equal to those of the conventional Cu-W heat sink and, in addition, the coefficients can be adjusted variably by changing the filling factor and arranging direction of the carbon fibers. In addition, the heat sink 1 can be manufactured by cutting a CFMMC composite material manufactured by an ordinary molten metal dipping method, the product size of the heat sink 1 can be decided without restriction, and the heat sink 1 can be manufactured at a low cost.