We report on transmission measurements on low temperature grown GaAs and standard GaAs for a spectral range 0.8-2.8 eV. We measured a drastic reduction of absorption due to annealing over the whole spectral range. The absorption changes depend on the annealing temperature and occur in two individual phases. Additional transmission measurements on samples without antireflection coating confirm our earlier results of an annealing induced refractive index change of Delta n approximate to 0.2.