A new technique has been developed to probe the region of apparent bis
tability due to a tunneling resonance in the characteristic of a semic
onductor asymmetric double-barrier structure. The measuring circuit us
es a voltage supply designed to have a load line with positive slope,
equivalent to a voltage source and negative series resistance. The app
earance of bistability and hysteresis in the characteristic is an arti
fact of the conventional measuring technique, which employs a load lin
e with negative slope. The complete characteristic is found to be a co
ntinuous Z-shaped curve between 50 and 150 K, corresponding to tristab
ility. Equivalent circuit models for the device and voltage supply pre
dict a narrow range of circuit parameters for which a static operating
point exists inside the tristable region.