The invention relates to the wet-chemical or electrolytic treatment of flat material, for example a wafer, which according to the prior art is treated by means of technically complex frames or grippers in treatment chambers. Particularly in the case of fracture-sensitive material such as silicon solar cells, the handling is very time-consuming, especially when the underside  of the material must not be wetted. According to the invention, the material (1) is placed without frames, grippers or holders above a vertically arranged treatment chamber (3) so that only the underside is wetted by the treatment liquid. As a result of a rotationally symmetric flow (4) on the underside (7) of the material placed on the surface of a treatment liquid, the adhesion forces acting horizontally on the material (1) cancel one another out. A lateral shift of the material does not occur. The limiters or lateral end stops which are usually used can therefore be dispensed with.