A method for improving the performance of a galvanic fuel cell type oxygen sensor comprises providing a pressure equalization port leading to the interior of an inner core housing that contains the membrane, the electrolyte and the anode and cathode electrodes and hermetically sealing the sensor housing except for its sample inlet port and its sample outlet port. By connecting the same vacuum source to both the pressure equalization port and the sample outlet port, the device's membrane is less subject to movement or rupture as gas samples are drawn in via the sample inlet port. A technique for ensuring a hermetic seal is also described.