A projection exposure apparatus for semiconductor lithography includes: a light source for generating optical used radiation by which structures arranged on a reticle can be imaged onto a wafer; a plurality of optical elements for guiding and manipulating the used radiation; and a plurality of position sensors for determining the position of at least some of the optical elements. At least some of the position sensors are arranged on a measurement structure that is at least partially decoupled mechanically and/or thermally from the further components of the projection exposure apparatus. The measurement structure has at least two mechanically decoupled substructures. The first substructure has a lower coefficient of thermal expansion than the second substructure. The second substructure has a greater stiffness than the first substructure.