This paper reports on ultra-low power 4–8 GHz (C-band) InP high-electron mobility transistor (HEMT) cryogenic low-noise amplifiers (LNAs) aimed for qubit amplification in quantum computing. We have investigated dc power dissipation in hybrid three-stage cryogenic LNAs using 100-nm gate length InP HEMTs with different indium content in the channel (65% and 80%). The noise performance at 300 K was found to be comparable for both channel structures. At 5 K, an LNA with 65% indium channel exhibited significantly lower noise temperature at any dc power dissipation compared to the LNA with 80% indium channel. The LNA with 65% indium channel achieved an average noise of 3.2 K with 23 dB gain at an ultra-low power consumption of 300 µW. To the best of authors’ knowledge, the LNA exhibited the lowest noise temperature to date for sub-milliwatt power cryogenic C-band LNAs.