In this paper, algeration of electical characteristics is analyzed when the operating temperature of MOSFET, BJT and CMOS/BiCMOS inverter is lowered from 300K to 77K. As the operating temperature is lowered, electric characteristics of MOSFET are enhanced generally but, those of bipolar transistor are degraded because current gain is reduced by BGN(Band Gap Narrowing) effect. For the inverter considered in this work, switching characteristics of PSA-BiCMOS inverter are enhanced by the electrical characteristics enhancement of MOSFET when the operating temperature is reduced to 200K, while under 200K, those of PSA-BiCMOS inverter are degraded because the degradation of BJT impacts on the inverter circuit.