The impedance and the response to a light-modulated signal are compared at p-InPV-3+/2+ semiconductorliquid junctions. The familiar recombination semicircle, seen in the complex-plane representation of the light-modulated response, is explained by electrochemical charge transfer (CT) phenomena. Transformable differential models are proposed which fit impedance and light-modulated data at bare and Ag-coated p-InP. Both spectroscopic methods verify an increase in the CT rate (the reason for higher solar-cell efficiency) and the capacity of the interface owing to the Ag coating. Unlike those at Ag-coated p-InP, Cr rates measured at the open-circuit potential at bare electrodes show a dependency on illumination intensity. Though both spectroscopic methods are based on identical theoretical principles, the number of parameters which can be determined at the system discussed is different (four parameters in impedance, two in the light-modulated method). Capacity data reported from several analytical methods are summarised and attributed to the same physical quantity.