The basis of the method is to measure the time taken for secondary electrons emitted from the specimen to reach a detector situated some way up the electron-optical column. This time depends on the potential of the point on the surface from which the electrons are emitted. Measurements previously reported by the authors were carried out on small specimens inserted into the final lens bore of a conventional scanning electron microscope. The work has now been extended so that measurments can be made on integrated circuit chips in standard dual-in-line packages. It has therefore been demonstrated that the technique is useful for voltage-contrast diagnostics on real specimens.