We report the results of a preliminary synchrotron radiation photoemission and Auger experiment on the Yb/Si interface, prepared insitu by depositing monolayers of Yb onto vacuum‐cleaved Si(111) surfaces at room temperature. Spectra were taken for the Si 2p and Yb 5p core levels at several different values of escape depth. The evolution of the valence band and the Si L2,3VV Auger line shape with coverage also were depth examined. The first monolayer of Yb is adsorbed onto the Si surface without apparent mixing or reaction. For 1.5–2 monolayers, there is evidence of chemical interaction from core level shifts and changes in the Si LVV line shape. At higher coverages, the surface becomes essentially Yb metal; the region of intermixing appears to be limited to 2–3 atomic layers at room temperature.