The influence of S, Se and Te on the capacitance–voltage ( C– U) and conductance–voltage ( G– U) characteristics of metal–insulator–GaAs structures has been investigated. It has been found that the result of passivation of the GaAs surface by chalcogenide elements (S, Se and Te) depends on the type of semiconductor. The presence of S and Se on the insulator–p-GaAs interface gives rise to a reduction of the total density of surface states, to a shift of the C– U and G– U characteristics at zero voltage and to a decrease in the frequency dispersion of the electrical characteristics and the conductance. Passivation of the n-GaAs surface causes a reverse effect.