  We argue that giant jumps of current at finite voltages observed in
disordered samples of InO, TiN and YSi manifest a bistability caused by the
overheating of electrons. One of the stable states is overheated and thus
low-resistive, while the other, high-resistive state is heated much less by the
same voltage. The bistability occurs provided that cooling of electrons is
inefficient and the temperature dependence of the equilibrium resistance, R(T),
is steep enough. We use experimental R(T) and assume phonon mechanism of the
cooling taking into account its strong suppression by disorder. Our description
of details of the I-V characteristics does not involve adjustable parameters
and turns out to be in a quantitative agreement with the experiments. We
propose experiments for more direct checks of this physical picture.
