In our paper “Determination of thickness and composition of thin AlxGa1-xAs layers on GaAs by total electron yield (TEY)” we described the principles of the determination of thickness t and Al concentration x employing TEY. The essential experimental quantities are the absorption edge jumps of the-eleraents measured in TEY-mode:Since the problem asks for the quantification of two unknowns (x,t), at least two TEYjumps are needed. The K jumps of Al and Ga deliver reliable information. From the theoretical approach1,2 of quantitative TEY a nearly linear relationship between the measured TEY jumps and the composition (in wt%) has to be expected. The As concentration varies over the interesting composition range 0<x<0.6 from approximately 50 to 60wt% and causes a similar variation of the TEY jump versus x. In combination with the statistical significance of the experimental data we neglect the TEY K jump information from As.