A process of fabricating a thin film semiconductor device is proposed, which is suitable for mass production and enables to lower the production cost. A first substrate is subject to anodization to form a porous layer thereon. Then, a thin film semiconductor layer is formed on the porous layer. Using the thin film semiconductor layer, a semiconductor device is formed, and wiring is formed between the semiconductor devices. After that, the semiconductor devices on the first substrate is bonded to a second substrate. The semiconductor devices are separated from the first substrate. Further, the semiconductor devices are electrically insulated by removing a part of the thin film semiconductor layer from the separated surface of the second substrate.