We study the effect of back-reaction on the evaporation of quantum black holes. The method used is based on quantum tunneling formalism as proposed in [4]. We give a more realistic picture by considering the fact that a black hole looses its energy while modes are tunneled outside the event horizon. It is shown how the tunneling quantum field modes affect the geometry and how this change in geometry is arrested in the quantum field. Exploiting this we calculate the modified (nonthermal)

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... n spectrum, associating energy fluxes and discuss various issues related with these. The results obtained here are often expected on physical grounds, but, importantly we find them in a quantitative manner.