Bimos semiconductor integrated circuit device including high speed vertical bipolar transistors

A semiconductor integrated circuit device having a bipolar transistor and an MOS transistor of a first conductivity type, comprising:

• a plirality of first region of a second conductivity type;
• a plurality of second regions of the second conductivity type each of said second regions formed on one of said first regions, an impurity concentration of each of said second regions being gradually decreased from the surface of the second region toward the corresponding first region;
• a vertical bipolar transistor having a collector region formed by said first region and one of said plurality of second regions;
• and
• a first conductivity type MOS transistor formed in another of said plurality of second regions,
• wherein the impurity concentration of each of said second regions is lower than an impurity concentration of the adjacent first region and a boundary of the first and second regions defines a minimum point of impurity concentration of the combination of the first and second regions, whereby said vertical bipolar transistor can operate at high speed without degrading operating characteristics of said first conductivity type MOS transistor.