Bright rings are observed in the scanning electron microscope (SEM) image when charge flashover in vacuum occurs on circularly bound polymethylmethacrylate surfaces using a SEM. The number and diameters of these rings vary with the applied observation voltage. These bright rings in the SEM correspond to the charge accumulation in the sample. The trapped charge transport in the insulator is either in the form of a large polaron or in the highly excited state. ©1995 American Institute of Physics.