Abstract: An apparatus for treating a wafer manufactured from semiconducting material, the apparatus comprising a first and a second housing part arranged for movement away front and towards each other, the two housing parts bounding a treatment chamber, while around the treatment chamber there is provided a first groove connected to gas discharge means, while in at least one of the two boundary surfaces there is provided a second groove connected to gas feed means, the first groove being located radially within the second groove, and, in use, the pressure created by the gas feed means being such that from the second groove, gas flows both in radial inward and in radial outward direction in the gap between the first and the second boundary surface.