To provide a structure capable of improving reliability of a surface mount connection area of a semiconductor device.

A mounting substrate for surface-mounting semiconductor devices 10a and 10b includes a hollow part 102 at a location sandwiched by an area of a first substrate layer 101a, corresponding to the backside of a first mounting pad and an area of a second substrate layer 101b, corresponding to the backside of a second mounting pad. This hollow part 102 reduces the thickness of each of the mounting areas, on which the semiconductor device 10a or 10b is mounted, to reduce stresses imparted on the semiconductor devices 10a and 10b by thermal deformation from the mounting areas of the respective substrate layers, thereby improving the reliability of the connection areas between each of the semiconductor devices 10a and 10b and corresponding one of the substrate layers.