Different samples originating from the same LEC ingot have been used in order to determine the variation of the EL2 concentration versus depth after different types of thermal annealing ( 450 and 850°C : the temperatures generally used in technological processes ). The annealing of EL2 near the surface at 850°C has been interpreted as the result of the deviation from the stoichiometry near the surface, due to [As] variation induced by vacancy diffusion. At 450°C, the annealing of EL2 can only be explained by the dissociation of a complex, followed by the migration of one of the constituants, confirming that the EL2 defect is the complex AsGa- Asi.