There is provided a method of removing trap levels and defects, which are caused by stress, from a single crystal silicon thin film formed by an SOI technique. First, a single crystal silicon film is formed by using a typical bonding SOI technique such as Smart-Cut or ELTRAN. Next, the single crystal silicon thin film is patterned to form an island-like silicon layer, and then, a thermal oxidation treatment is carried out in an oxidizing atmosphere containing a halogen element, so that an island-like silicon layer in which the trap levels and the defects are removed is obtained.