We report numerical simulations of typical experimental conditions under which current‐voltage (I‐V) measurements of resonant‐tunneling diodes are conducted. We find that curve tracer measurements can cause bistability and hysteresis in the negative differential resistance (NDR) region. We also find that dc measurements can produce oscillations which distort the shape of theI‐Vcurve. When the series resistance is large, there are three states for a given bias in the NDR region because of the folding of theI‐Vcurve. We believe this phenomenon, extrinsic tristability, to be the source of extrinsic bistability.<lz> <lz> <lz>