This paper reports on the first demonstration of a reconfigurable complementary-metal-oxide-semiconductor (CMOS) oscillator based on microelectromechanical system (MEMS) resonators operating at four different frequencies (268, 483, 690, and 785 MHz). A bank of multifrequency switchable AlN contour-mode MEMS resonators was connected to a single CMOS oscillator circuit that can be configured to selectively operate in four different states with distinct oscillation frequencies. The phase noise (PN) of the reconfigurable oscillator was measured for each of the four different frequencies of operation, showing values between -94 and - 70 dBc/Hz at a 1-kHz offset and PN floor values as low as -165 dBc/Hz at a 1-MHz offset. Jitter values as low as a 114-fs root mean square (integrated 12 kHz-20 MHz) and switching times as fast as 20 μs were measured. This first prototype represents a miniaturized solution (30 times smaller) over commercially available voltage-controlled surface-acoustic-wave oscillators and potentially has the advantage of generating multiple stable frequencies without the need of cumbersome and power-consuming phase-locked-loop circuits.