Effects of ultrasounds propagating perpendicular to the direction of a uniform dc magnetic field in degenerate semiconductors such asn‐type InSb have been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. It is found that the absorption coefficient and change in sound velocity oscillate with the dc magnetic field for the nonparabolic band structure. However, the absorption coefficient vanishes and no oscillations can be observed in the magnetic‐field dependence of the change in sound velocity for the parabolic band structure. The discontinuity in the frequency dependence of the change in sound velocity can only be observed in the nonparabolic band structure.