A semiconductor integrated device of the invention can enhance a radiation resistance. In an exemplary embodiment, the semiconductor integrated device includes a semiconductor supporting substrate, an insulation layer provided on the semiconductor supporting substrate, and a silicon thin film provided on the insulation layer. A predetermined region in the silicon thin film that is adjacent to the boundary between the insulation layer and the silicon thin film (i.e., boundary neighboring region) has an impurity-concentration-increased region. In this region, the impurity concentration becomes higher as the position approaches the boundary.