Effects of ultrasonic waves propagating at an angle &Vthgr; relative to the direction of a dc magnetic field in nondegenerate piezoelectric semiconductors such asn‐type InSb have been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The interaction of conduction electrons with waves is via deformation‐potential and piezoelectric couplings. Results show that variation of the direction of the magnetic field with respect to the direction of propagation of ultrasonic waves will affect the ultrasonic absorption coefficient and change in sound velocity. Therefore the absorption coefficient and change in sound velocity depend strongly on the dc magnetic field, the sound frequency, the temperature, and the direction of the propagation of ultrasonic waves relative to that of the field.