A 3.1~10.6 GHz ultra-wideband low-noise amplifier (UWB LNA) with excellent phase linearity property (group-delay variation is only ±15.8 ps across the whole band) using standard 0.18 μm CMOS technology is reported. Both high and flat power gain (S₂₁) and low and flat noise figure (NF) frequency responses are achieved by tuning the pole frequencies and pole quality factors of the second-order gain and NF frequency responses to approximate the maximally flat condition simultaneously. The LNA dissipates 11.8 mW power and achieves input return loss (S₁₁) smaller than -10.2 dB, high and flat S₂₁ of 12.52±0.81 dB, and low and flat NF of 2.87±0.19 dB over the 3.1~10.6 GHz band. To the author's knowledge, this is one of the lowest NFs ever reported for a 3.1~10.6 GHz UWB CMOS LNA. The measured 1-dB compression point (P_1dB) and input third-order inter-modulation point (IIP3) are -16 dBm and -6.5 dBm, respectively, at 6 GHz.