The diffusion length (L) of minority carriers was determined from contrast of linear defects. Dislocation contrast was measured by EBIC at room temperature versus bias of a Schottky diode. It was shown for the first time that the slope of the contrast curves depends onL. The requirement to the SEM regime and EBIC geometry were formulated in a way to avoid influence of surface recombination on the measurements and diminish the role of other side effects as well.