High-electron-mobility transistors (HEMTs) based on 2-D electron gases (2DEGs) in III-V heterostructures have superior mobility compared with the transistors of silicon-based complementary metal-oxide-semiconductor technologies. The large mobility makes them attractive not only for low-noise and high-power microwave applications but also for low-power applications down to deep cryogenic temperatures. Here, we report on the design and characterization of a low-power HEMT LC Colpitts oscillator operating at 11 GHz whose minimum power consumption is 90 μW at 300 K and 4 μW at 1.4 K. The fully integrated oscillator is based on a single HEMT transistor having a gate length of 70 nm and realized using a 2DEG in In 0.7 Ga 0.3 As. The power consumption of the realized oscillator is the lowest reported in the literature so far for an LC oscillator operating in the same frequency range. In order to investigate the behavior of the oscillator, we also performed a detailed characterization of a stand-alone HEMT transistor from 1.4 to 300 K with a static magnetic field from 0 to 8 T. From the extracted values of the transistor parameters, we estimate and compare the minimum power necessary to start-up oscillations for two different Colpitts topologies.