The design and measurement results of 3–5 GHz fully integrated ultra-wideband (UWB) CMOS LNA are presented. To boost the transconductance of the LNA and to reduce circuit area effectively, we eliminate a source degeneration inductor using resistive-feedback cascode structure. The implemented UWB LNA shows peak gain of 10.8 dB, more than 10 dB of input return loss, and a noise figure of 3.3–4.2 dB from 3 to 5.1 GHz with power dissipation of 14 mW. The input P1dB and input IP3 (IIP3) at 4 GHz are about −6 dBm and +4 dBm, respectively. For low cost, the LNA has been fabricated using a 0.18-μm thin metal CMOS process with top metal thickness of 0.84 μm.