The change in surface potential resulting from wear at ultralow loads using Kelvin probe microscopy is studied. Samples studied include single-crystal silicon (100), single-crystal silicon (100) lubricated with fully bonded Z-DOL (a perfluoropolyether). The effects of relative humidity (RH) as well as that of load and number of cycles during wear on the change in surface potential have been investigated. It is believed that the removal of either contaminant layer, natural oxide layer or lubricant during few wear cycles gives rise to the initial change in surface potential. As the number of cycles and/or load increases, the material is removed from the silicon surface by subsurface fatigue wear and stresses beneath the silicon surface resulting in subsurface structural changes which are responsible for further change in the surface potential.