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In this paper, monolithic microwave integrated circuit (MMIC) broadband low-noise amplifiers (LNAs) for cryogenic applications based on a 100-nm metamorphic high-electron mobility transistor (mHEMT) technology in combination with grounded coplanar waveguide are reported. A three-stage LNA, operating in 4-12 GHz and cooled to 15 K exhibits an associated gain of 31.5 dB ± 1.8 dB and average noise temperature of 5.3 K (NF=0.079 dB) with a low power dissipation of 8 mW. Additionally another three-stage LNA 25-34 GHz cooled to 15 K has demonstrated a flat gain of 24.2 dB ± 0.4 dB with 15.2 K (NF=0.22 dB), average noise temperature, with a very low power dissipation of 2.8 mW on chip. The mHEMT-based LNA MMICs have demonstrated excellent noise characteristics at cryogenic temperatures for their use in radio-astronomy applications.