Abstract: A pressure sensor assembly includes an external housing unit; a sensor unit received within the external housing unit, the external housing unit has an external surface including a mounting surface; a sensing element mounted within the sensor unit and including a pressure-sensing surface; a substrate upon which the mounting surface is mounted; an air passage to enable air to impinge on the sensing element; and a filling passage, separate from the air flow passage, for the introduction of an encapsulation material onto the sensor unit, during assembly. The encapsulation material covers at least a part of the external surface of the sensor unit but does not cover the pressure-sensing surface of the sensing element which remains directly exposed to air within the air passage.