A hydrogen ion-implanted layer is formed on the surface side of a first substrate which is a single-crystal silicon substrate. At least one of the surface of a second substrate, which is a transparent insulating substrate, and the surface of the first substrate is subjected to surface activation treatment, and the two substrates are bonded together. The bonded substrate composed of the single-crystal Si substrate and the transparent insulating substrate thus obtained is mounted on a susceptor and is placed under an infrared lamp. Light having a wave number range including an Si—H bond absorption band is irradiated at the bonded substrate for a predetermined length of time to break the Si—H bonds localized within a “microbubble layer” in the hydrogen ion-implanted layer, thereby separating a silicon thin film layer.