A gas sensor is provided for use in a hazardous explosive atmosphere present continuously or for a long time. The gas sensor is not provided with a pressure-proof housing and is provided with at least one catalytic or semiconductor measuring element (3) in a hollow body (6) defining the measuring element (3) against the environment. The hollow body has breathing openings (4) and wherein the ratio of the area of the breathing openings to the total area of the hollow body equals, furthermore, at most 0.8 or the hollow body is porous with a porous hollow body material having a pore size according to ISO 4003 equal to at most 2 mm.