Photoelectrochemical characteristics of the p-silicon/potassium ferri-ferrocyanide electrolyte interface have been investigated by in situ Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy. The photoelectrode p-Si, which is IR transparent, was used as the ATR element. Comparison to the i-silicon/potassium ferri-ferrocyanide interface shows the effect of space charge layer. Cyclic voltammetry corresponding to in situ FTIR-ATR spectra indicated that the adsorption of ferri-ferrocyanide ions is affected by the applied voltage and the intensity of illumination. The results showed that the redox ion pair can cause electron-hole recombination at the semiconductor/electrolyte interface. Electron exchange between semiconductor and redox couple through the C=N bridge was observed. Possible mechanism and structures of intermediates are discussed.