The expression of an effective conductivity tensor for the magnetoacoustic amplification in extrinsic, nondegenerate semiconductors has been derived by the Boltzmann equation taking proper account of the Hall effect. This expression can be applied to any values of the frequency of acoustic waves and of the magnetic field in the classical regime. Detailed discussion of the Doppler‐shifted ultrasonic cyclotron resonance (DSUCR) is given by takingn‐InSb as an example. It is shown that the effective mass and the relaxation time of electrons can be determined by DSUCR. A brief discussion is also given on the magneto‐acoustoelectric instability inn‐InSb.