We report an electrochemical study of the reduction of ferricyanide at p-Si(100) and p-Si(111) electrodes in aqueous alkaline solutions. It is shown that this reaction can give information about charge transfer through thin anodic oxide films and about the mechanism of Si etching. Etch rate measurements in combination with electrochemical experiments reveal that, at oxide-free chemically etching electrodes, ferricyanide is partly reduced by reaction with an intermediate of the Si etching process. Analogies between the ferricyanide reduction and the electrochemical etching of silicon indicate that the reactive intermediate is most likely to be formed during the breaking of the Si-Si back bond.