Voltage contrast scanning electron microscopy has been exploited to investigate the operating stability of conductive polymer composite resettable fuse devices. It has been shown that the technique enables the active region of the device to be imaged and, hence, its position and shape to be compared after a succession of operating cycles and as a consequence of the position of the attached surface electrodes. This leads to a useful diagnostic tool for the investigation of the configuration of such devices and the morphology of the conductive polymer composite material of which they are made.