A package for accommodating a semiconductor element includes a heat releasing
member
having a mounting portion for a semiconductor element, a frame having a wiring
conductor, and a lid attached so as to cover the mounting portion. In the heat
releasing member, a plurality of through-metal members made of a copper are buried
in the mounting portion of a substrate made of a matrix of tungsten or molybdenum
and copper to another surface. Copper layers are joined at least to upper and lower
surfaces of a portion in which the through-metal members are buried, and a cross-section
area of each of the through-metal members is gradually increased from the center
side of the substrate to a joint portion with the copper layers.
