The capabilities of automatic ellipsometry are demonstrated for semiconductor technology i.e. thin films processing on optical polished silicon and gallium arsenide wafers. Real-time evaluation of a film deposit is shown in the case of the plasma oxidation of a silicon substrate through a thin film of calcia stabilized Zr02 (CSZ). The trajectory in the (ψ , Δ) plane indicates that a Si02 layer is developed between CSZ and Si. Structural damages occur in this layer above a critical voltage, corresponding to large deviations of the ellipsometric trajectory. In the cases when in situ examination is not feasible, a non-destructive depth profiling of the thin film can be obtained by varying the energy of the incident light, using a spectroscopic ellipsometer. The Si3N4/Si interface is examined on Si3N4/Si02/Si structures (the active part of a MNOS device) as well as thermally nitrided silicon wafers. Optical absorption due to uncompletely nitrided Si tetrahedra is found in both cases. Also examined are implanted layers in GaAs. Because the incident ions locally transform the crystalline GaAs into an amorphous state, with a very distinct dielectric function, it is possible to derive from the spectroscopic ellipsometry data a depth profile of the ion induced damages.