A method of manufacturing a semiconductor integrated circuit device of the bipolar type of the MOS type or an integration of the two types having high integration and high performance, in which the circuit includes a first device region of which the side surface and entire region of the lower portion of the active region are made of silicon oxide and a second device region of which the side surface and a part of the lower portion of the active region are made of silicon oxide. According to the present invention, a transistor whose bottom portion is opened and a transistor whose bottom portion is not opened can be freely provided on a substrate, thereby dividing the transistors into a transistor to which a voltage can be supplied from the substrate and a transistor to which the voltage can not be supplied from the substrate, so that the wiring which has been conventionally needed can be reduced. In addition, in such transistors which are completely separated, the parasitic effect with the circumference is completely prevented so that excellent characteristics can be provided.