What is required for the functional testing of modern high-density and fast IC and large scale integration (LSI) circuits is a method which has a time resolution in the subnanosecond region and a spatial resolution in the submicrometer region. Furthermore, the test probe must be easy to position on the circuit. To meet these requirements, a combined stroboscopic SEM-microcomputer test system has been developed. A microcomputer is used for striking the electron beam to a point of interest on the specimen surface, sampling and storing the signal waveforms, performing an operation of signal processing, and generating a data display or data output in numerics. Following a system description, application to a MOS LSI (4 k bit static random access memory-RAM) in the MHz regions is reported to demonstrate the efficiency of the system.