We present the Rayleigh instability of low-frequency (in comparison with the ion-gyrofrequency) electrostatic waves in multi-ion species plasmas containing equilibrium density gradient and transverse ion-sheared flows caused by the dc electric field. For this purpose, multi-fluid equations are used to obtain the governing equations for two-dimensional convective cells and pseudo-three-dimensional drift waves in a non-uniform magnetoplasma. Standard procedures are then employed to study the Raleigh instability. Thresholds and growth rates are obtained. Applications to Hall thrusters are discussed.