We have investigated controlling the phase velocity of a surface acoustic wave (SAW) by a microelectromechanical switch fabricated on a high coupling piezoelectric substrate. The principle is based on the interaction of the evanescent surface potential of the SAW with the conductive switch. In theory tuning of the velocity in the range given by ν0 and νm, i.e. the velocity for a SAW on a free and metallized substrate, is possible. We have achieved up to 17.6 m/s (0.44 %) velocity tuning on 128°YX LiNbO3. A maximum velocity sensitivity of Δν/ν of 15×10-3/V and phase sensitivity of 700°/V was measured. This is five orders of magnitude larger than values obtained for electrical field tuning.