A composite substrate for a semiconductor includes a handle substrate 11 and a donor substrate bonded to a surface of the handle substrate 11 directly or through a bonding layer. The handle substrate 11 is composed of an insulating polycrystalline material, a surface 15 of the handle substrate 11 has a microscopic central line average surface roughness Ra of 5 nm or smaller, and recesses 6 are formed on the surface of the handle substrate.