Hydrogen peroxide in solution changes the transient current response to pulse illumination of the n-Si \ anodic oxide I electrolyte interface in buffered neutral electrolyte. The effect is understandable if the anodic oxide is slightly porous and is then attributable to an increase in the electron-hole pair recombination rate at the oxide electrolyte contact. It is easily measured by intensity modulated photocurrent spectroscopy (IMPS), varying the frequency of intensity modulation of the light source and determining the frequency at which the out-of-phase component of the photocurrent response is a maximum. A simple technique is illustrated using a variable-frequency current drive to a light-emitting diode as the modulated light source. The feasibility of glucose measurement using IMPS to determine the hydrogen peroxide generated by the enzyme-catalysed oxidation of glucose in the presence of oxygen is demonstrated. The possibility of developing a spatially-addressable biosensor array which is easily integrated with silicon microelectronics is noted.