A circuit substrate of a grounding structure of a semiconductor device according to the invention has a plurality of connection pads and a grounding wiring. The semiconductor device has a semiconductor substrate having one side face and the other side face opposite thereto, an insulating film formed thereon, an SOI integrated circuit provided thereon and including a plurality of connection pads, and electrodes for external connection each of which is connected to the corresponding connection pad. The semiconductor device has the external connection electrodes connected to the respective connection pads of the circuit substrate by a face-down bonding scheme. An under-filling material is provided between the semiconductor device and the circuit substrate, and there is provided a connection member which connects the other side face of the semiconductor device with the grounding wiring of the circuit substrate, and is made of a conductive material.