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. The heat sink comprises a pair of Cu—Mo composite layers and a Cu layer stacked in a thickness direction so that the Cu layer is interposed between the Cu—Mo composite layers or comprises three or more Cu—Mo composite layers and two or more Cu layers alternately stacked in the thickness direction so that two of the Cu—Mo composite 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. Such a clad structure achieves high thermal conductivity together with a low coefficient of thermal expansion.