A optoelectronic semiconductor device, mountable on and electrically connectable to an electro-optical wiring board, a substrate thereof having a light input/output through-hole and electric connection through-holes, the light input/output through-hole being not formed in a stressed area of the circuit wiring board, but formed in a non-stressed area of the circuit wiring board, the stressed area being an area where a stress is larger in value than the mean value of stresses caused in the circuit wiring board by a difference in coefficient of thermal expansion between the circuit wiring board and the electro-optical wiring board when the electrode on the semiconductor optoelectronic device is mechanically fixed to and electrically connected to the electro-optical wiring board.