Abstract: A semiconductor integrated circuit device having at least one bipolar transistor comprises a semiconductor substrate of monocrystalline silicon having a main surface; an isolation oxide layer selectively formed on the main surface so as to surround an active region of the main surface; a first silicon layer formed on the active region and extending on the isolation oxide layer and a second silicon layer stacked on the first silicon layer, wherein a collector region of a bipolar transistor is formed on the active region of the first silicon layer, the intrinsic base region is formed on the active region of the second silicon layer, and a base-lead out region which is electrically connected with the intrinsic base region is formed of the first and second silicon layers over the isolation oxide layer.