A chopped‐light spot has been used to explore the photoresponse of siliconp‐njunction surfaces. Anomalous channel responses extending in some cases to distances of 100 mils or more, have been observed on accumulation layer and intrinsic barrier surfaces. The phase shift of the induced ac photocurrent is measured as a function of the distance of the light spot from the junction, and phase shifts of more than 380° have been observed for the anomalous channels. Experimental evidence is offered to show that the excessive phase shift is due to multiple trapping of the injected carriers at surface interface states. Additional evidence indicates that the anomalous channels are a result of an interaction of the fringing field with the slow surface states.