Low-pressure silicon epitaxial technology is applied to high-speed bipolar logic LSIs to reduce autodoping from heavily-doped substrates. As a result, collector-base stray-capacitance (CTc) is remarkably reduced. In this report, the dependence of CTC on epi-layer thickness and the CTCdependence of tpd(propagation delay time) are also mentioned. The propagation delay time, tpdis reduced by about 10-15% due to the reduction of CTCcaused by applying low pressure epitaxy. The obtained minimum value of tpdis about 0.35 ns.