DC bias dependent acoustic resonance phenomena have been observed in micromachined tunable thin film capacitors based on Ba0.3Sr0.7TiO3 (BST) thin films. The antiresonance frequency is only weakly dc bias dependent, whereas the resonance frequency exhibits a strong dependence on the applied dc bias. The resonance frequency shifted by 0.8% for a frequency of about 3.44 GHz and an applied of 333 KV/cm. At the same time the electromechanical coupling constant k(t)(2) increased to 1.8%. The experimental observations correlate well with the theoretical predictions derived from the free energy P expansion using Landau theory.