A placement base (100) of a semiconductor device (90) comprises a body (10), to which a radiation agent (80) having viscosity is applied and on which a semiconductor device (90) is disposed, and a protrusion (20), which is placed in an outer periphery of the body (10) and on which the semiconductor device (90) is not disposed. A detective groove (30) for introducing the radiation agent (80) is provided on a surface of the protrusion (20).