The early work of Brattain and Bardeen [1] demonstrated that under illumination, a semiconductor surface develops a potential which can be measured with non-contact, capacitive coupling. Since then, the surface photo-voltage (PV) effect has received sporadic experimental as well as theoretical considerations. A number of experiments have been reported (with and without contacts) which make use of both dc and ac surface PV (see, for example, Ref. 5). In the latter form, the incident light is modulated at frequencies ranging from a few Hz to a few MHz. Both the dc and ac embodiments of the surface photo-voltage effect have been used to study various minority and majority carrier transport mechanisms in the presence of various degrees of inversion (or accumulation) of the semiconductor surface.