The effect of nonparabolicity on the amplification of surface phonons in piezoelectric semiconductor films is investigated quantum mechanically in the GHz frequency region. Numerical results are obtained for ann‐type GaAs epitaxial layer on a semi‐insulating GaAs substrate at 77 °K. Results show that the amplification is enhanced for the nonparabolic band structure due to the nonlinear nature of the energy band in semiconductors.