In a lithographic projection apparatus, a liquid supply system maintains liquid in a space between a projection system of the lithographic projection apparatus and a substrate. A sensor positioned on a substrate table, which holds the substrate, is configured to be exposed to radiation when immersed in liquid (e.g., under the same conditions as the substrate will be exposed to radiation). By having a surface of an absorption element of the sensor, that is to be in contact with liquid, formed of no more than one metal type, long life of the sensor may be obtained.