A Trench isolation technology has been developed and applied to high-speed bipolar LSI production. In general, the wafer surface after a conventional ploy-Si Chemical-Mechanical-Polishing (CMP) is contaminated with silica particles and chemical impurities. These contaminations produce some unexpected patterns and crystal defects in the wafer surface layer after oxidation. It is difficult to remove them by the conventional cleaning techniques. Therefore, we have established the new post CMP cleaning method, using the electrolytic ionized water containing chemical additive of a small quantity. The anode water has the cleaning effect for the metallic and organic contaminations, and the cathode water has the removing effect for the particles and the etching effect for the poly-Si surface. For this new cleaning process, it is important to avoid the chemical mechanical damages on the surface and to control the surface roughness. Our experimental work has been focused on the large numbers of the remaining particle and the surface roughness using a particle counter and an atomic force microscopy (AFM). We herein report the properties of the electrolytic ionized water and the examined results of poly-Si surface after CMP process. It was found that the electrolytic ionized water is effective for surface control, and the new cleaning process is useful for CMP process.