[en] A detailed analysis of self-consistent potentials, electric fields, electron distributions, and transport properties of dual-channel (DC) n-Al${}_{0.3}$Ga${}_{0.7}$N/GaN/i-Al${}_x$Ga${}_{1-<!--\; ???\; -->x}$N/GaN high-electron-mobility transistors (HEMTs) is performed in this article. The 2D electron gas (2DEG) densities and mobility states limited by different scattering mechanisms in channel 1 and channel 2 are obtained, with varying values of doping concentrations, ambient temperatures, Al components, and thicknesses of the back barrier layer. The reduced and increased 2DEG densities are respectively observed in channel 1 and channel 2 with growing Al fractions and thicknesses of the Al${}_x$Ga${}_{1-<!--\; ???\; -->x}$N layer. Alloy disorder scattering exhibits a superior effect on carriers in channel 2 due to the lower barrier height and higher permeable electrons, which together with the interface roughness scattering severely depends on the thicknesses and Al fractions of the back barrier layer. Polar optical phonon scattering becomes important at higher temperatures. The trend of individual mobility in channel 1 is exactly opposite to that in channel 2. The parameter variation of the back barrier layer can effectively change the scattering characteristics of the main channel. Low-temperature mobilities of n-Al${}_{0.3}$Ga${}_{0.7}$N/GaN/i-Al${}_x$Ga${}_{1-<!--\; ???\; -->x}$N/GaN HEMTs under varied doping concentrations are also obtained. Finally, the results are verified by comparison with the technology computer-aided design simulations for DC HEMTs. (© 2024 Wiley‐VCH GmbH)