We report the dispersion characteristics of ScAlN/GaN high-electron-mobility transistors (HEMTs) with various epitaxial designs. Devices were fabricated on both ternary (ScAlN) and quaternary (ScAlGaN) materials. The effects of a GaN capping layer was also investigated. We report similar DC and RF performance for all wafers, but significantly worse dispersion which occurs on the quaternary samples. We observe a total gate and drain lag for the ScAlN wafer to be 49% while the ScAlGaN with and without the GaN cap had 10 and 12% dispersion, respectively.