The second harmonic generation (SHG) proved to be a very promising characterization technique for dielectric-semiconductor interfaces because it is sensitive, non-destructive, can be applied directly on wafer, at different stages of wafer processing. The method, based on non-linear optics effects, is measuring a signal encompassing the "static" electric field at the dielectricsemiconductor interface which is directly related to the oxide charges Q ox and to the interface state density D it. A general methodology for Q ox and D it extraction from SHG measurements requires (i) calibration based on parameters obtained by classical electrical methods and (ii) modeling to capture the optical propagation phenomena that impact the SHG signal. In this paper, we discuss these issues based on a review of our recent advances on how to exploit SHG for dielectrics on semiconductor characterization.