In recent years, interest in semiconductor electrochemical electrodes has increased because of their possible uses in solar energy conversion systems, integrated circuit technology, and many other applications. In this work, we have characterized a Si/fluoride electrolyte interface. Measured transient flatband potential data were available. Starting from these measurements, we have developed a model to calculate the charges inside the oxide layer formed at the Si/HF electrolyte interface. In the first step, we assumed that the oxide charges decay due only to etching. The results obtained show a decreasing positive charge distribution from the electrolyte side to the Si side. To show the effect of surface states on the charge distribution inside the oxide, a model in which we separated the oxide bulk charges from the fast electronic surface states at the Si oxide interface was developed. We found that the surface states affect only the value of the charge distribution at the very early phase of oxide etching. To confirm the validity of the model, we extended it to explain measured data for the variation of the transient electrochemical cell capacitance and current when the potential is stepped from an anodic value to a negative probe value. The results obtained are in good agreement with experiments.