The effect of a bias electric field on the phase velocity of Lamb waves propagating in a piezoelectric plate has been investigated in order to develop an electroacoustic voltage sensor. Experiments were performed onYXandYZLiNbO3Lamb‐wave delay lines, used as the stabilizing element in the feedback loop of an oscillator, by measuring the fractional frequency change produced by a bias electric field normal to the plate surfaces. The results obtained have shown that Lamb‐wave sensors can exhibit a higher sensitivity and a better linearity than the corresponding Rayleigh‐wave devices.