||AlxGa1-xN/GaN heterostructures with different Al compositions were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The compositions of Al in the AlGaN layer were confirmed to be 13 %, 28 %, and 30 % using high resolution X-ray diffraction (HRXRD). The fabricated AlxGa1-xN/GaN high-electron mobility transistors (HEMTs) with different Al compositions were fabricated, characterized, and compared using Hall Effect, DC, and low-frequency noise (LFN). The device with highest Al composition showed the improved sheet resistance (Rsh) due to the enhanced carrier confinement and the reduced off-state/gate leakage currents caused by the increased Schottky barrier height (SBH). On the other hand, the noise level and the calculated trap density (Nt) were obtained to the lowest values when the device has 13 % of Al composition. This is because the dislocation density in AlxGa1-xN barrier layer decreases as the Al composition decrease. In spite of the Al composition, the fabricated devices exhibited the 1/ƒ noise behavior and the carrier number fluctuation (CNF) model, which is proved by the curves of both (SId/Id2) versus (gm/Id)2 and (SId/Id2) versus (Vgs – Vth).