We investigated the growth behavior of GaN grown on AlN along with V/III ratio and pressure variation, and found out the lateral growth regime for the fully coalesced channel layer of the AlN-based double-hetero structure high electron mobility transistor (HEMT). When the V/III ratio increases and pressure decreases, compressive stress in the GaN channel increases, and pit formation occurs to release the stress. The AlN-based HEMT structure was grown and the device was fabricated with an optimized channel layer. The two-dimensional electron gas mobility, sheet density, and sheet resistance were 1480 cm 2 V− 1 s− 1, 1.32× 10 13 cm− 2, and 319 Ω/sq., respectively, at room temperature. The device was characterized; direct current output result showed that the maximum current was∼ 620 mA mm− 1, on-resistance was 6.4 Ω mm, transconductance was∼ 140 mS mm− 1, and current on/off ratio was∼ 10 4, respectively.