Provided is a heat sink that has a clad structure of a Cu—Mo composite material and a Cu material and has a low coefficient of thermal expansion and high thermal conductivity. A heat sink comprises three or more Cu layers and two or more Cu—Mo composite layers alternately stacked in a thickness direction so that two of the Cu layers are outermost layers on both sides, wherein each of the Cu—Mo composite layers has a thickness section microstructure in which flat Mo phase is dispersed in a Cu matrix. The heat sink has a low coefficient of thermal expansion and also has high thermal conductivity in the thickness direction because the thickness of each of the Cu layers which are the outermost layers is reduced, as compared with a heat sink of a three-layer clad structure having the same thickness and density.