To overcome such a problem that the heat generated when a semiconductor element operates is not efficiently radiated outside, resulting in thermal destruction of the semiconductor element.

The package for housing a semiconductor element comprises a base substrate 1 which comprises on its upper surface a placement part 1 on which a semiconductor element 4 is placed, a ceramic frame-like insulator 2 which is fitted on the base substrate 1 to enclose the semiconductor element placing part 1a and comprises a wiring layer 6 to which each electrode of the semiconductor element 4 is connected, and lid 3 which is fitted on the frame- like insulator 2 and seals air-tightly the inside of the frame-like insulator 2. The base substrate 1 is formed by allowing a baked porous body comprising tungsten powder of average particle size 50-100 μm, excluding particles whose particle size is 25 μm or less, to be impregnated with copper, with the baked porous body comprising tungsten being 75-95 wt.% and copper being 5-25 wt.%.