This paper presents a high-gain differential CMOS low noise amplifier (LNA) for 3.1-10.6GHz ultra-wideband receivers. A novel structure that combines capacitive cross-coupling common-gate topology with common-source topology is proposed, which increases the power gain greatly and imposes little impact on other performances of the LNA.The LNA is designed in the TSMC 0.18µm CMOS technology. Post-layout simulation results show that the LNA achieves a power gain of 14.9 ∼ 16dB and a noise figure of 3.5 ∼ 4.9dB with a current consumption of 6.3mA from a 1.8V power supply. The layout area is 0.7 × 0.9mm².