Bistable current–voltage characteristics caused by competition of tunneling through and field-enhanced thermionic emission across a single barrier are investigated in an n–-GaAs/Al0.34Ga0.66As/n+-GaAs structure. The S-shaped part of the characteristic persists in the whole temperature regime between 4.2 and 300 K in accordance with theoretical predictions. The delay and switching times of the transition from the low- to the high-conducting state are investigated as a function of the applied voltage and compared with simulations. The observed timescales are much longer than expected from theory, which indicates the presence of additional deep centers or interface states. ©1996 American Institute of Physics.