To provide a semiconductor device enabling an efficient heat dissipation not only from the topmost LSI chip but also from the LSI chips of the lower part in a laminated of two or more LSI chips.

In the semiconductor device with two or more LSI chips 2 overlying a relay substrate 1, thermally conductive underfill resin 10 is formed between LSI chips 2 adjoined up and down, or between the lower surface of the lowermost LSI chip and substrate 1. Generated heat of the LSI chip 2 is radiated to the external atmosphere by contacting the surface of the topmost LSI chip 2, and each side of the LSI chip 2 and the side of thermally conductive underfill resin 10, respectively, and by reaching the heat sink 8, with the opposite side front surface of the LSI chip 2 of heat dissipating sheet 9 in contact with inside, through the heat dissipation sheet 9. The heat sink 8 covers the whole laminated structure as well.

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