A low-power inductorless 1:4 DEMUX and a 4:1 MUX for a 90 nm CMOS are presented. The DEMUX can be operated at a speed of 25 Gb/s with the power supply voltage of 1.05 V, and the power consumption is 8.9 mW. The area of the DEMUX core is $29;{ imes};40;{mu}m^2$. The operation speed of the 4:1 MUX is 13 Gb/s at a power supply voltage of 1.2 V, and the power consumption is 4 mW. The area of the MUX core is $30;{ imes};18;{mu}m^2$. The MUX/DEMUX mainly consists of differential pseudo-NMOS. In these MUX/DEMUX circuits, logic swing is nearly rail-to-rail, and a low $V_{dd}$. The component circuit is more scalable than a CML circuit, which is commonly used in a high-performance MUX/DEMUX. These MUX/DEMUX circuits are compatible with conventional CMOS logic circuit, and it can be directly connected to CMOS logic gates without logic level conversion. Furthermore, the circuits are useful for core-to-core interconnection in the system LSI or chip-to-chip communication within a multi-chip module, because of its low power, small footprint, and reasonable operation speed.