Clean, flat, strain‐free surfaces of Si, Ge, , and of the faces of were prepared by scanning jets of chemical polishing reagents across one side of the rotating slices. The faces of were electrochemically polished in the same apparatus. It was found possible to reduce the central areas of large diameter Si slices to thicknesses of tens of microns while retaining thick, mechanically strong rims with this technique by masking the edges of the slices. Whole slices of Si were also reduced to uniform thicknesses of under 20 µm by this technique.