PURPOSE: To provide a semiconductor device and its manufacturing method, wherein a semiconductor substrate, with which no crack occurs and heat radiation drop is suppressed to a minimum, with a via-hole farmed from its rear side, is die-banded on a conductive base body.

CONSTITUTION: A rear surface electrode 7 consisting of an Au plated layer is formed so that bath the rear surface of a GaAs substrate 1 whose thickness is 150μm and the internal periphery surface of a hemisphere via-hole 6 formed at the GaAs substrate 1 are coated, and only on the part of the rear surface electrode 7 coating the internal periphery surface, over a specified distance (d) from the bottom of the via-hole 6 in the direction of thickness of tone GaAs substrate 1, an Ni electrolytic plating layer 12 is selectively formed. Then under this condition, through the rear surface electrode 7, the GaAs substrate 1 and a die pad 100a are soldered together with an AuSn solder 8.