To provide a package for housing a semiconductor element having excellent transmission characteristics of a high-frequency signal and heat-dissipation properties and inhibiting the warping generated by heat, and a semiconductor device.

The package for housing the semiconductor element has a base body 8 with a placing section 8a for the semiconductor element 4, a frame body 1 surrounding the placing section 8a, and a plurality of lead terminals 2. Shelf sections 3 for supporting and fixing the inside sections of the frame body 1 of the lead terminals 2 are formed on the internal surface in the frame body 1. Cavity sections 11 are formed from sites, where the central sections of the inside sections of the frame body 1 of the lead terminals 2 are positioned, to the underside of the frame body 1 respectively in the shelf sections 3. The lead terminals 2 contain lead terminals 2a for transmitting the high-frequency signal and lead terminals 2b for a grounding fitted at equal intervals on both sides of the lead terminals 2a while width-broading sections 2d in which widths are broadened gradually towards the outside of the frame body 1 are formed in the frame body 1 in the lead terminals 2a.