Locating fault origins of defective logic LSls requires expensive equipment, such as electron beam testers and LSI testers. In order to maximize the utilization of such equipment in achieving high fault analysis throughput as well as to save manpower, the authors are developing an automatic fault tracing system which locates the fault origin overnight without human assistance through control of an electron beam tester and an LSI tester. The system traces backwards via the fault propagation path and locates the fault origin by comparing the behavior of a faulty LSI sample with that of a good LSI sample. Sample exchange in a vacuum chamber is achieved through a dual chip loading mechanism. After initial setting, fault location is accomplished without human assistance by fully automated operations, such as fine tuning SEM images of LSI surfaces, aligning points by robust pattern matching between SEM images and layout data, acquiring voltage contrast images with high contrasts and judging logical voltage levels from the images. A prototype version of this system successfully backtraced to the fault origin of an LSI with 20 k gates in 8 hours.