An object of the present invention is to provide a semiconductor device built-in substrate, which can be made thin and can suppress occurrence of warpage. The present invention provides a semiconductor substrate which is featured by including a first semiconductor device serving as a substrate, a second semiconductor device placed on the circuit surface side of the first semiconductor device in the state where the circuit surfaces of the first and second semiconductor devices are placed to face in the same direction, and an insulating layer incorporating therein the second semiconductor device, and which is featured in that a heat dissipation layer is formed at least between the first semiconductor device and the second semiconductor device, and in that the heat dissipation layer is formed on the first semiconductor device so as to extend up to the outside of the second semiconductor device.