The conceptual design and measurement of a monolithic bulk acoustic wave (BAW) oscillator with conventional plastic QFN packaging is presented. The unique Silterra technology allows the integration of high frequency BAW resonators on top of a standard 0.13µm CMOS technology [1]. The oscillator circuitry is placed under the BAW resonator for smaller form factor and reduction of parasitics. The oscillator has tunable gain and phase and the output signal can be divided by a factor from 8 to 240. The measured phase noise performance of the 2.22GHz oscillator is -85dBc/Hz at 10 kHz offset frequency and a -158dBc/Hz noise floor. The integrated phase jitter from 12 kHz to 20 MHz is fs. This low noise oscillator allows the development of high performance and high frequency signal sources based on MEMS BAW oscillators replacing the traditional LC CMOS solutions.