A high-Q micromechanical device such as a capacitor and method of tuning same by electrostatically moving the capacitor's dielectric are provided. The high-Q, tunable, micromechanical capacitor is realized using an IC-compatible, electroplated-metal, surface-micromachining technology and demonstrates quality (Q-) factors in excess of 290--the highest reported to date for on-chip tunable capacitors at frequencies near 1 GHz. When combined with on-chip (or off-chip) high-Q inductors, these tunable capacitors are expected to be useful for not only low-phase noise integrated VCO applications, but also for tunable, low-loss, RF filters and tunable matching networks, both key functions capable of enhancing the multi-band programmability of wireless communication handsets. The key feature in this design that makes possible such high on-chip Q is the method for capacitive tuning, which is based on moving the dielectric between the capacitor plates, rather than moving the plates themselves, as done in previous designs. One version of the design achieves a measured Q of 291 at 1 GHz (C=1.2l pF) with a tuning range of 7.7% over 10 V of control voltage, and an expected self-resonant frequency (SRF) of 19 GHz. In another version of the design, with a wider tuning range of 40% over 10 V, a Q of 218 is achieved at 1 GHz (C=1.14 pF).