Taking advantage of the interferometric technique described in ref.1 and relying on the Luke and Cheng model for the electron-hole transient recombination process2), we propose an all optical measurement procedure able to separate the bulk contribution from the surface one to the recombination lifetime in silicon wafers. According to ref.2 and to the results obtained from many numerical simulations, the electron-hole transient recombination process can be described by an appropriate multi-mode decay provided that the bulk lifetime (Â¿B) and the surface recombination velocity (SRV) can be regarded as constant quantities. Indeed, this condition holds true if the carrier concentration is constant during the entire decay process. This last requirement poses an upper limit to the excess carrier concentration that should be considered to monitor the electron-hole transient evolution process. In particular, the injected carriers Â¿N must be a ``small perturbation'' to the regime carrier density N present in the semiconductor. Our simulations indicate that the small signal condition is fulfilled when the quantity Â¿N/N is smaller than 0.1.