Raman instability of the Stokes component of the scattered electromagnetic wave has been investigated in an n-type piezoelectric semiconductor in the presence of a large transverse magnetostatic field. The general dispersion relation has been obtained following the coupled-mode theory and considering that the scattering results not only from the molecular vibrations produced owing to the pump wave at a frequency equal to that of the transverse-optical phonons but also from the electron plasma wave. The analysis has been applied to both cases of isotropic (B0=0) and magnetoactive (B00) plasmas. The threshold value of the pump amplitude necessary for the onset of instability and the growth rate of the unstable mode well above the threshold have been obtained analytically for B0=0 and B00. It is observed that a large transverse magnetostatic field can reduce the threshold value of the pump amplitude and increase the growth rate of the unstable Raman mode at an electric field amplitude greater than the threshold value. Numerical estimates have been made for n-InSb crystal at 77 K. The crystal has been irradiated with a pulsed 10.6-µm CO2 laser to obtain the necessary electric field. The analytical as well as the numerical results have been compared with those of Sen while studying Brillouin instability in n-type magnetoactive piezoelectric semiconductors. © 1980 The American Physical Society.