A low‐energy electron diffraction (LEED) system has been used to study the energy spectra of Auger electrons from clean and alkali‐covered Ge and Si surfaces. Auger bands characteristic of the substrates were observed for the clean surfaces and the deposition of submonolayer coverages of K and Cs introduced new bands characteristic of the respective alkali. It is shown that a surface impurity in a quantity as small as 0.1 monolayer can be detected and identified by this measurement.