We present the analysis, design, and measurement results of a low-noise, low-power MEMS oscillator at 20 MHz. The oscillator consists of a high-Q differential resonator, which is wire-bonded to a high-gain CMOS transimpedance amplifier (TIA). Measurement results show that the TIA achieves a tunable gain from 12 kΩ to 69 kΩ. The phase noise floor of the oscillator's output voltage is at -131 dBc/Hz, while the differential peak-to-peak swing can be varied between 160 mV and 1700 mV by an on-chip automatic level control (ALC) loop. The TIA, fabricated in a 0.35-μm CMOS process, occupies an area of 0.15 mm² and dissipates 6.9 mW from a 2.5 V supply.