A new method of deriving the random fraction in a disordered channel : rom dechanneling experiments is described. In this method backscattering spectra obtained at two different doses are employed, with an assumption on the dose dependence of the defect concentration. The method is applied to the experimental data forB-implanted Si and it is found that the obtained random fraction is similar to the result of the diffusion calculation made by the present authors. The depth profiles of defects are also obtained and compared with the result of theoretical calculations.