A theory for amplification of acoustic waves in the presence of dc and oscillating electric fields in a piezoelectric semiconductor is developed. Acoustic gain constants for bothksl≪1 andksl≫1 are derived, whereksis the wave vector for the acoustic wave, andlis the mean free path for the electron in the piezoelectric medium. As expected, the expressions for the gain constants reduce to those for the ordinary acoustic amplifier case when the applied oscillating electromagnetic signal is zero. The theory indicates that it is possible to transfer modulation from the electromagnetic wave to the acoustic wave.