PURPOSE: To provide the titled powder having high thermal conductivity and good electrical insulating properties and suitable for use in sealing electronic components, by covering the surface of each particle of copper powder with the cured film of an electrical insulating resin.

CONSTITUTION: Copper powder having a particle size of 50W100μm is mixed with a soln. of an electrical insulating resin (e.g. polyvinylpyrrolidone) dissolved in a solvent such as methylene chloride. The mixture is spray-dried to remove the solvent. The resulting dried product is heated at a predetermined temp. to obtain the desired thermally conductive powder for use in a sealing resin, wherein the surface of each particle of the copper powder is covered with a 10W30μm thick cured film of the electrical conductive resin. 40W150pts.wt. said powder is blended with 100pts.wt. resin component to obtain a sealing resin.