The characteristic intrinsic properties of silicon surfaces are strongly related to the dangling bonds, and their presence again are due to the different possible reconstructions. It is possible to create surfaces on which the dangling bonds are removed or changed by adsorption of gas atoms or metal atoms. Such surfaces may exhibit new, tailorable properties, making them interesting for device applications. In this report, the properties of hydrogen and oxygen terminated n-type Si(111) surfaces are compared with respect to Cs adsorption, and seen against those of the Si(111) 7 × 7 surface. The techniques include core level and valence band photoemission with synchrotron radiation at the Aarhus storage ring, spectroscopic optical second harmonic generation and LEED. It is found that the hydrogen terminated (1 × 1) surface has practically no free dangling bonds and is unpinned. As a result the position of the band edge is strongly lowered with Cs adsorption. This surface is stable against Cs adsorption and shows a highly enhanced electron emission upon radiation with photons as a result of the lowered workfunction. The (monolayer) oxygen terminated surface is electronically stable and shows a pinning of the surface potential resisting the movement of the band edge with adsorption of Cs, despite a reaction between Cs and oxygen. For the clean surface direct interactions between Cs and Si surface atoms create new interface states at the Fermi level. A number of less significant differences between these surfaces are also pointed out.