We report on the annealing of InP and GaAs substrates, placed side by side, in a hydrogen atmosphere. This annealing is done with and without arsine, and also in the presence of elemental arsenic replacing GaAs. This simple technique shows the stabilization of InP by the presence of GaAs in a temperature range between 550 and 750 degree C. It gives information about active species present during substrate annealing. The results obtained show that the protecting species of column V elements, dimers or tetramers, behave differently than the ones resulting from the decomposition of the V hydride.