The application of high-resolution electron energy-loss spectroscopy (HREELS) to semiconductor surfaces and interfaces is reviewed with main emphasis on recent results obtained from semiconductors with the technically relevant (100)-orientation like Si, Ge, Ge/Si-alloys, GaAs, and InP. In particular this paper describes aspects of the atomic structure of differently prepared surfaces before and after hydrogenation. In addition, it is shown that HREELS can be used to gain detailed information about different semiconductor interface parameters, e.g. carrier concentrations, depletion layer widths, band bending, mobility etc.