A new formation process of anodizable structures ofn,n+, andn−silicon for the production of silicon‐on‐insulator (SOI) structures is described. In this process, proton implantation is employed to produce a high donor concentration layer near the surface ofn‐type silicon substrates, and nitrogen ion implantation is employed to define highly resistive islands in the high donor concentration layer. The anodization of silicon in HF solution to form porous silicon and the consequent oxidization of the porous silicon to form silicon dioxide is restricted to the high donor concentration regions. It is demonstrated that silicon islands with a width of 50 μm and a thickness of 0.55 μm are successfully isolated by an oxidized‐porous‐silicon layer with a thickness of 2.25 μm.