Using a custom-made numerical simulation tool, we performed a systematic study of the energy distribution of the interface trap density in a GeSn MOS structure and of their effect on the electrical characteristics such as C-V and impedance spectra. Interface traps with various densities of states and energies in the bandgap have been investigated and the application of the conductance method was assessed. Based on a theoretical analysis, we obtained, as key results, direct connections between microscopic parameters of the structures and experimentally accessible features of the simulated macroscopic quantities. A straightforward relationship between the interface state density and the peaks in the conductance response is also highlighted. The dependence of the peak characteristics on the trap states was identified, as well as the effects of traps extending over large energy ranges in the bandgap. (C) 2013 Elsevier B. V. All rights reserved.