We have developed a new method of evaluating Si suface micro-roughness, by forming thin oxide in HCl/H2O2 solution and then measuring the concentration of chlorine atomes and the total charge in this oxide. It is shown that this oxide does not affect the surface micro-roughness, and the surface concentration of chlorine atoms incorporated in this oxide and the total oxide charge are proportional to the surface microroughness, obtained by AFM. From this correlation, it is possible to evaluate the surface micro-roughness for large areas compared with the areas of AFM measurement.