Abstract: 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.