A semiconductor substrate and a light-valve semiconductor substrate is provided so as to prevent the threshold value of a MOS transistor on a single-crystal silicon device forming layer from increasing in order to obtain a MOS integrated circuit with a high reliability even for over a long time of operation. A semiconductor substrate and a light-valve semiconductor substrate comprising a single-crystal silicon thin-film device forming layer 5001 formed above an insulating substrate 5004 through an adhesive layer 5003 and an insulating layer 5002 formed on the single-crystal silicon thin-film device forming layer, wherein heat conductive layers 5201 and 5202 made of a material with a high heat conductivity are arranged between the single-crystal silicon thin-film device forming layer and the adhesive layer and on the insulating layer.