Header for semiconductor device, and semiconductor device

A header for a semiconductor device, comprising:

• a main body section having an upper surface, and a cavity formed in the upper surface;
• a heat dissipation section provided on the upper surface of the main body section;
• and
• a wiring board provided inside the cavity,
• wherein the wiring board includes
• a substrate having a first principal surface, and a second principal surface provided on an opposite side from the first principal surface,
• a first conductor pattern provided on the first principal surface, and having a mounting section on which a semiconductor element is mounted, and
• a second conductor pattern provided on the second principal surface, and bonded to an inner wall surface of the cavity and the heat dissipation section,
• wherein the wiring board and a portion of the first conductor pattern respectively extend beyond the heat dissipation section when viewed in a thickness direction of the wiring board, perpendicular to the first and second principal surfaces.