A high‐gain Ka‐band 0.18‐μm CMOS low‐noise amplifier with semicircle stacked grounded coplanar waveguide (SCS‐GCPW) structure transmission line is proposed. SCS‐GCPW transmission line is adopted to reduce the signal loss by shaping the electric fields under the signal line especially at microwave and millimeter wave applications. The SCS‐GCPW demonstrated a similar electric field distribution of coaxial cable and achieved a substrate dielectric attenuation constant of 0.075 Np/m. It is superior to 0.081 Np/m and 0.144 Np/m of traditional microstrip transmission line and CPW transmission line, respectively. By adopting the low loss SCS‐GCPW transmission line, the Ka‐band LNA demonstrated a 24.5 dB gain together with a noise figure (NF) of 7.5 dB at 33 GHz operation. The measured output power 1 dB compression point (P1 dB) was −2 dBm. The dc power consumption was 40 mW and chip size was 0.6 × 1 mm2 for this Ka‐band LNA. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1131–1134, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25910