Method for manufacturing an SOI wafer. On a monocrystalline silicon wafer, forming protective regions having the shape of an overturned U, made of an oxidation resistant material, the protective regions covering first wafer portions. Forming deep trenches in the wafer which extend between, and laterally delimit the first wafer portions, completely oxidizing the first wafer portions except their upper areas which are covered by the protective regions, to form at least one continuous region of covered oxide overlaid by the non-oxidized upper portions. Removing the protective regions, and epitaxially growing a crystalline semiconductor material layer from the non-oxidized upper portions.