Ge(3d) and Si(2p) core level photoemission intensities were measured to monitor the coverage of Ge(001) and Ge(111) surfaces during the interrupted deposition of a thin Si film at room temperature and upon annealing. Annealing treatments were performed at temperatures up to a maximum of 880 K and interrupted a few times to allow for core level measurements. The Ge(3d) core level intensity was found to almost recover to its initial value upon annealing while the Si(2p) intensity decreased ∼60%. Intensity changes were observed at temperatures from 680 K upwards. It is concluded that above 680 K a significant diffusion of Si into Ge occurs, although at higher temperatures island formation or surface roughening also takes place.