In a method for manufacturing a micromechanical semiconductor component, e.g., a pressure sensor, a locally limited, buried, and at least partially oxidized porous layer is produced in a semiconductor substrate. A cavity is subsequently produced in the semiconductor substrate from the back, directly underneath the porous first layer, using a trench etch process. The porous first layer is used as a stop layer for the trench. Thin diaphragms having a low thickness tolerance may thus be produced for differential pressure measurement.