A mathematical model to describe the impedance behaviour of the amorphous semiconductor Schottky barrier in the high band bending region is proposed. The model is based on the admittance theory of the amorphous silicon Schottky barrier and it is valid in the polarisation region where the semiconductor displays a Mott-Schottky like behaviour. We have applied the model to the characterisation of very thin (10-44 nm) amorphous oxides formed electrochemically on titanium. The calculated parameters are shown to be in good agreement with those obtained from the classical (low band bending) amorphous silicon Schottky barrier theory for the same oxides. A comparative discussion on the advantages and handicaps of each model is carried out.