Let us consider the surface composition of the binary alloy, where the surface compositionR1is considered to be different from the bulk inside compositionR2and also the segregation region thickness isT. In this model it is possible to count the Auger signals considering the contributions of an attenuating primary beam and the secondary electrons which are backscattered and forwardscattered. Using the theory, we have calculated theseR1for the reported experimental results of the Ag‐Au binary alloy as a function ofT. The calculated Ag compositionR1are compared with the ISS (Ion Scattering Spectroscopy) results that are said to be the most surface sensitive technique. When the bulk Ag content is less than 50 at. %, the Ag segregation region thicknessTis considered to be one monolayer (2.58 A˚ ∼ an average layer spacing,d3=M/6.02×1023&rgr;, whereM= atomic mass and &rgr; = specific mass or density). However, when the bulk content is greater than 50 at. %,Tlies between one and two monolayers (2.58 and 5.16 A˚). The usual method that uses a relative sensitivity factor only estimates the surface average composition in the depth of the mean free path of the Auger electrons. However, this method can estimate the surface compositionR1as well as the segregation region thicknessT.