Al-Ga interdiffusion, carbon acceptor diffusion, and hole reduction were studied in carbondoped Al0.4Ga0.6As/GaAs superlattices (SL). Al-Ga interdiffusion was found to be most prominent for Ga-rich annealing, with the hole concentrations in the SL almost intact during annealing. For As-rich annealing, the interdiffusivity values, DAI.Ga, are in approximate agreement with those predicted by the Fermi-level effect model, and the hole concentrations in the SL decreased dramatically after annealing. By analyzing the measured hole concentration profiles, it was found that both carbon acceptor diffusion and reduction have occurred during annealing, with both depending on As4 pressure values to the one quarter power. These As4 pressure dependencies indicate that carbon diffuses via the interstitial-substitutional mechanism while hole reduction is governed by a precipitation mechanism.