Header for semiconductor package, and semiconductor package

A semiconductor package comprising:

• a header for a semiconductor package, including:
• an eyelet having a through hole penetrating the eyelet from an upper surface to a lower surface of the eyelet,
• a first lead inserted inside the through hole, and
• an insulating substrate disposed on the upper surface of the eyelet, and provided with a first through hole at a position overlapping one end of the first lead in a plan view, wherein the insulating substrate has a thermal conductivity lower than a thermal conductivity of the first lead, a first conductive layer is formed on an inner wall defining the first through hole, and the first conductive layer extends to an upper surface of the insulating substrate, the one end of the first lead is electrically connected to the first conductive layer, and a space is provided above the one end of the first lead inside the first through hole;
• a cooling element disposed on the upper surface of the eyelet;
• a substrate disposed on the cooling element;
• and
• a light emitting element mounted on the substrate, wherein:
• an interconnect electrically connecting to the light emitting element is formed on the substrate, and
• the interconnect is electrically connected to a portion of the first conductive layer extending to the upper surface of the insulating substrate via a wire member.