We propose InGaAs-based junctionless transistor (JLT) with dual-spacer dielectric and a gate length (LG) of 5 nm for low power loss and high frequency mobile network system. The dual-spacer dielectric consisting of HfO2 and SiO2 increases an effective gate length (Leff) due to a high fringe field. The increased Leff reduces significantly the off-state current (Ioff) by suppressing leakage currents formed by the drain-induced barrier lowing (DIBL) and band-to-band tunneling (BTBT) phenomenons. Further, the JLT with the dual-spacer dielectric obtains a lower gate capacitance (Cgg) in comparison to the JLT with the single-spacer dielectric HfO2 because SiO2 in the dual-spacer dielectric decreases an outer fringe capacitance (Cof). Due to a lower Cgg, the JLT with the dual-spacer dielectric also improved intrinsic delay time (τ), cut-off frequency (fT), and maximum oscillation frequency (fmax).