PURPOSE: To obtain a mounting structure which has high heat sink efficiency, preferable workability, and ready handing and assembling by using a heat transfer sheet cladded by an indium on both side surfaces of a core metal sheet having large thermal conductivity.

CONSTITUTION: A heat transfer sheet 8 is inserted between a heat sink substrate 2 and a module mounting surface 5, and formed by cladding thin indium 10 on both side surfaces of a core metal sheet 9 having large thermal conductivity such as, for example, a thin copper plate, Since such a sheet 8 has a thin indium layer, the profile working or the opening of a threaded hole 11 can be facilitated, for example, by pressing in the same manner as the case of only the sheet 9, and the handling such as a transporting can be also facilitated. The indium 10 is very closely contacted with the large irregular surfaces of the substrate 2 and the module mounting surface 5, and intruded into the fine irregular surface as compared with the large irregular surface due to the deformation of the soft sheet 9. Accordingly, the contacting thermal resistance can be reduced in the same manner as the case of using only the indium sheet.