We present experimental investigations of current filamentation in n‐GaAs films in the regime of low‐temperature impurity breakdown. Using a laser‐scanning microscope, we were able to reconstruct current filaments in biasing regions of multistability. It is shown that discontinuities and hysteresis frequently observed in current–voltage characteristics are due to the interaction of filaments with material imperfections. In particular filaments remain in energetically unfavourable configurations when squeezed or pinned by defects.