The theoretical background of the Schottky barrier capacitance of disordered semiconductors is recalled and the temperature, frequency, and bias dependence of the capacitance is illustrated on hydrogenated amorphous silicon (a-Si:H), hydrogenated polymorphous silicon (pm-Si:H) and hydrogenated microcrystalline silicon (muc-Si:H). Both a-Si:H and pm-Si:H follow the same trends, with a lower defect density in pm-Si:H. Quite different features are observed in muc-Si:H, and are related to different defect levels and to the two-phase constitution of the material. Finally, the capacitance analysis is reviewed in the framework of the amphoteric dangling bond states, where the influence of both defect transitions is emphasized.