This paper presents two K-band low-noise amplifiers (LNAs) in 65-nm CMOS using the proposed RF junction varactors as the ESD protection devices. The junction varactors are customized for the RF ESD applications with accurate equivalent circuit models. The experimental results demonstrate excellent second breakdown currents (It2) and high ratios of the ESD level to parasitic capacitances (VESD/CESD) . Using the dual-diode topology, the first LNA demonstrates an over 2-kV Human-Body-Model (HBM) ESD protection level with a noise figure (NF) of 2.8 dB and a peak gain of 14.3 dB at around 24 GHz under a power consumption of only 7 mW. By incorporating an RF junction varactor as the extra gate-source capacitance at the input stage as a part of the ESD network, the second LNA presents an enhanced failure current level up to 2.6 A (corresponding to an HBM ESD level of 3.9 kV), and a Charge-Device-Model (CDM) ESD level up to 10.7 A, characterized by the Very Fast Transmission Line Pulse (VFTLP) tests. The second LNA shows a NF of 3.2 dB and a power gain of 13.7 dB, also under 7 mW.