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AlGaN-GaN heterostructures with different Al concentrations (20, 27, and 35%) were grown by metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates. Ti-Al-Ti-Au ohmic contact optimization was investigated at different temperatures and annealing time. Heterojunction field effect transistors (HFET) with a gate length of 0.25 μm were fabricated. Low contact resistances of 0.2, 0.26, and 0.33 Ω·mm were obtained for HFET device samples with Al concentrations of 20, 27, and 35%, respectively. For Al concentration of 20, 27, and 35%, the AlGaN-GaN devices exhibited extrinsic transconductances of 143, 152, and 210 mS/mm, Idss of 398, 566, and 784 mA/mm, unity cutoff frequencies (fT) of 24.9, 34.6, and 50 GHz and maximum oscillation frequencies (fMAX) of 54.9, 61.8, and 100.9 GHz and minimum noise figures (Fmin) of 2.01, 1.47, and 1.02 dB at 12GHz, respectively. The calculated minimum noise figures have a good agreement with the measured values for all the devices with different Al mole fractions. The noise analysis shows that intrinsic noise of these AlGaN-GaN FETs plays a prominent part in the noise behavior because of improved device parasitics.