An apparatus for treating wafers, provided with at least one treatment chamber, the apparatus being provided with a feeding section in which wafers contained in a wafer storage box can be fed into the apparatus, the apparatus being provided with a wafer handling apparatus, by means of which wafers can be taken out of the wafer storage boxes so as to be treated in the treatment chamber, and the apparatus being provided with at least one sensor box arranged such that the wafer handling apparatus can feed a wafer into the sensor box through an opening provided for that purpose in the at least one sensor box, and the at least one sensor box being arranged to carry out measurements at a wafer, wherein the at least one sensor box is movably arranged and the apparatus is provided with a sensor box handling apparatus arranged to move the at least one sensor box from a storage position to a measuring position.