A semiconductor device package is comprised of a metal base for receiving a semiconductor
device, a metal frame joined at its lower face to the metal base, a seal ring joined
at its lower face to an upper face of the metal frame, and a metal lid joined to
an upper face of the seal ring. The upper face of the seal ring is formed, at its
at least two sides facing each other, into a concavely warped shape as viewed in
vertical cross section, and the maximum warpage of the upper face of the seal ring
is not more than 0.2% of the length of the side of the upper face.
