In this paper, we present a prestress vertical comb drive resonator with a frequency tuning capability. The resonator consists of three sets of comb fingers, which act as driving electrodes. The comb fingers are fabricated along with a composite beam. One end of the composite beam is clamped to the anchor, whereas the other end is elevated vertically by the residual stress. A clamped force, which is formed by a DC voltage, is utilized to restrain the vibration of the composite beam. By applying a DC clamped voltage and a driving voltage in different electrodes, the resonator exhibits different frequency responses. The device is fabricated through a 0.35 mm complementary metal-oxide-semiconductor (CMOS) process with a post-CMOS micromachining process. Experimental results indicate that the initial resonant frequency of the device is 18.6 kHz, and the maximum frequency tuning range up to 28.5% is obtained. The resonator device can recover its original frequency without causing any structural damage.