The method comprises the steps of providing a semiconductor body or substrate (1) with a recess or trench (2) in a main surface (10), applying a mask (3) on the main surface, the mask covering the recess or trench, so that the walls and bottom of the recess or trench and the mask together enclose a cavity (4), which is filled with a gas, and forming at least one opening (5) in the mask at a distance from the recess or trench, the distance (6) being adapted to allow the gas to escape from the cavity via the opening when the gas pressure exceeds an external pressure.