Effect of Hall current on the thermal instability in a boundary layer is
studied. The criterion on the position marking on the onset of longitudinal vortices is defined in the present paper. The results show that the onset position characterized by the Grashof number depends on the Prandtl number, the Reynolds number, the wave number, the Hall parameter, and the Hartmann number. The flow becomes more stable as the magnetic field increases. However, the destabilizing effect is found on the flow when the Hall current is applied. The results of the present numerical prediction show reasonable agreement with the experimental data with in the case of zero Hartmann number and Hall parameter in the open literature.