Nanowire photoconductors have shown extraordinarily high photo gains(up to 8 orders of magnitude)[1] which are closely related to the density and distribution of surface trap states[2].Mapping out surface trap states in the semiconductor bandgap is important to understand the high gain phenomenon of nanowire photoconductors.But it is extremely challenging to do so at single nanowire level using the traditional capacitive techniques based on metal-insulator-semiconductor(MIS)structures[3] and deep level transient spectroscopy(DLTS).