Abstract: A semiconductor fabrication process uses a buried, oxygen-rich layer as a stop etch in a trench isolation area, with minimal masking. According to one embodiment, the process involves applying a mask to protect selected portions of a silicon-based substrate, and then using the mask to implant an oxygen-based substance into unmasked portions of the substrate, thereby forming a buried oxygen layer at a selected depth within the substrate. The same mask is then used in an etching process to form the desired trench structure. The depth of the trench is defined as a result of terminating the etch process upon reaching the buried oxygen layer.