This research aims to determine whether a GaN HEMT device made on SiC substrate has a memory effect. To accomplish this, the intermodulation distortion technique with the separation frequency (Δf) of the two-tone input signals was applied at three different frequency levels, one at f1 = 53 MHz and the other two at f1 = 3.6 GHz and 7 GHz, with a varying range of a few megahertz of 1, 5, and 10 MHz. For this, the 0.15 × (4 × 50) μm2 GaN HEMT was chosen due to its favourable DC and RF figures of merit. The effect of the separation frequencies on the fundamental, IMD2 and IMD3 output powers are demonstrated. The findings show a significant effect of the separation frequency (Δf) on the output power and the nonlinear products within this frequency range.