We report on experimental and theoretical investigations of the dark current behavior inn‐type GaAs/AlAs/Al0.3Ga0.7As double‐barrier quantum wells (DBQW). The dark current perpendicular to the 50‐period DBQW structures shows evidence of tunneling through the 2‐nm‐wide AlAs tunnel barriers and thermionic emission across the 25‐nm‐wide AlGaAs layers. The temperature dependence is in good agreement with our numerical simulations, using an effective escape rate of 2.2×1014s−1. The dark current is further modified by internal electric fields caused by an asymmetric dopant distribution, which partially arises from a dopant segregation during epitaxial growth. We also present a theoretical simulation showing how the dark current versus voltage dependence is influenced by these space‐charge fields. ©1995 American Institute of Physics.