We present two-dimensional simulations of current filaments in the regime of low-temperature impurity breakdown in thin n-GaAs films under the influence of a magnetic field perpendicular to the sample plane. Our simulations show that current filaments are bent by the Lorentz force and their width and curvature increase with magnetic-field strength. Significant asymmetry of the electric fields is observed at opposite filament boundaries. These results agree well with experiments. It is also revealed by simulations that impurity breakdown is accelerated by the presence of an external magnetic field. This is attributed to a finite Hall field inside the filaments. ͓S0163-1829͑97͒00203-8͔

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