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High-performance AlGaN/GaN high electron-mobility transistors with 0.18m gate length have been fabricated on a sapphire substrate. The devices exhibited an extrinsic transconductance of 212 mS/mm, a unity current gain cutoff frequency () of 101 GHz, and a maximum oscillation frequency (MAX) of 140 GHz. At ds = 4 V and ds = 39 4 mA/mm, the devices exhibited a minimum noise figure (NF min) of 0.48 dB and an associated gain () of 11.16 dB at 12 GHz. Also, at a fixed drain bias of 4 V with the drain current swept, the lowest NF min of 0.48 dB at 12 GHz was obtained at ds = 40 mA/mm, and a peak of 11.71 dB at 12 GHz was obtained at ds = 60 mA/mm. With the drain current held at 40 mA/mm and drain bias swept, the NF min increased almost linearly with the increase of drain bias. Meanwhile, the values decreased linearly with the increase of drain bias. At a fixed bias condition (ds = 4 V and ds = 40 mA/mm), the NF min values at 12 GHz increased from 0.32 dB at 55 C to 2.78 dB at 200 C. To our knowledge, these data represent the highest and MAX , and the best microwave noise performance of any GaN-based FETs on sapphire substrates ever reported.