This paper describes a technique that makes it possible, by analyzing the capacitance-voltage characteristics of metal-insulator-semiconductor or metal-semiconductor structures, to determine the concentration of the background donor impurity in undoped i-In0.53Ga0.47As layers with a thickness less than the width of the space charge region in the near-surface region of the semiconductor in strong inversion mode. Keywords: InGaAs, MIS structure, capacitance-voltage characteristic, dopant, space charge region.