A composite is obtained by press-molding a mixed powder comprising 20-50 vol % of a metal powder and 50-80 vol % of a diamond powder for which a first peak in a volumetric distribution of particle size lies at 5-25 μm, and a second peak lies at 55-195 μm, and a ratio between the area of a volumetric distribution of particle sizes of 1-35 μm and the area of a volumetric distribution of particle sizes of 45-205 μm is from 1:9 to 4:6, thereby obtaining a composite having a high thermal conductivity and a coefficient of thermal expansion close to that of semiconductor devices, which is easy to mold into a prescribed shape.