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VIST1)(Vertically Isolated Self-aligned Transistor) Technology and its application to ICs and LSIs are presented. With a walled emitter structure, reduction of the emitter-collector leakage of the VIST, consisting of a bird's beak-free oxide-isolated structure and an inactive base (low ρ) self-aligned to the polysilicon emitter, has been made possible. E-C leakage current was measured on a fabricated bipolar integrated circuit array containing one hundred elements/chip. It was found that the thicker the side wall oxide, the remarkably smaller the E-C leakage current became. These results were well corresponded to the density of defects which were observed by Sirtl etching of stripped wafers. Applicability of the VIST to actual device was investigated in a high-speed frequency divider and an 8×8 multiplier/accumulator.