PURPOSE: To protect a bonding wire against a shortcircuit trouble keeping a heat sink excellent in heat dissipating property by a method wherein a metal layer whose oxide film functions, at least, as an insulator is provided onto a heat sink board, an electrode is patterned thereon, and the part other than the electrode is oxidized.

CONSTITUTION: A metal layer 13 whose oxide film functions, at least, as an insulator is provided onto a heat sink board 1, and electrode 3 is patterned thereon, and the part other than the electrode 3 is oxidized. For instance, a Cr layer 14 and an Au layer 15 are evaporated on the rear side of an Si board 1, an Al layer 13, a Cr layer 12, and an Au layer 15 are successively evaporated on the surface of the Si board 1, and the Cr layer 12 and the Au layer 11 other than a part where the electrode 3 is formed are removed through photolithography and etching. In succession, the exposed Al layer 13 is oxidized using an oxidizing agent to form an Al2O3 film 4 on it, and thus a heat sink on which the electrode 3 is patterned can be obtained.