With increases in frequency and density of RISC microprocessors due to rapid advances in architecture, circuit and fine device technologies, power consumption becomes a bigger concern. Supply voltage should be reduced from 5 V to 3.3 V. In this paper, several novel circuits using 0.5µm BiCMOS technology are proposed. These can be applied to a superscalar RISC microprocessor at 3.3 V power supply or below. High speed and low power consumption characteristics are achieved in a floating-point data path, an integer data path and a TLB by using the proposed circuits. The three concepts behind the proposed high speed circuit techniques at low voltage are summarized as follows. There are a number of heavy load paths in a microprocessor, and these become critical paths under low voltage conditions. To achieve high speed characteristics under heavy load conditions without increasing circuit area, low voltage swing operation of a circuit is effective. By exploiting the high conductance of a bipolar transistor, instead of using an MOS transistor, low swing operation can be got. This first concept is applied to a single-ended common-base sense circuit with low swing data lines in the register file of a floating and an integer data path. Both multi-series transistor connections and voltage drops by Vth of MOS transistors and Vbe of bipolar transistors also degrade the speed performance of a circuit. Then the second concept employed is a wired-OR logic circuit technique using bipolar transistors which is applied to a comparator in the TLB instead of multi-series transistor connections of CMOS circuits. The third concept to overcome the voltage drops by Vth and Vbe is addition of a pull up PMOS to both the path logic adder and the BiNMOS logic gate to ensure the circuits have full swing operation.