According to one embodiment, a semiconductor package includes: a first metal body on which a part of a waveguide structure is formed; a second metal body including a mounting area for a semiconductor device and disposed on the first metal body; a line substrate on which a signal transmission line configured to communicate a waveguide with the semiconductor device mounted on the mounting area is formed; and a lid body disposed at a position facing the first metal body, interposing the second metal body and the line substrate. The lid body is made of resin, on which a structure corresponding to another waveguide structure on an extension of the waveguide structure in the first metal body is formed. The structure includes a metal-coated inner wall surface.