The electronic structure and layer resolved density of states have been calculated for the Ge/RbF/GaAs slab using the linear combination of atomic orbitals procedure. In this epitaxial system, the RbF layer is used as an insulating intralayer, and the aim of the work is to study the electronic states introduced by this intralayer. Two crystallographic orientations of the slab were investigated : (100) and (111). It has been found that the RbF layer ensures the insulation of the two semiconductors, so their electronic structures do not influence each other. Besides, an inert interface, which preserves the electronic structure of a clean, unreconstructed semiconductor surface and does not introduce any interface states, can be obtained when two polar (as GaAs/RbF(111)) or two non-polar (as Ge/RbF(100)) surfaces are in contact.