An observation of quantum interference effect in photocurrent spectra of a weakly coupled bound‐to‐continuum multiple quantum well photodetector is reported. This effect persists even at high biases where the Kronig–Penney minibands of periodic superlattice potential in the continuum are destroyed. Our results show that electrons remain coherent over a distance of 40–50 nm. The observation was used to investigate electric field domain formation induced by sequential resonant tunneling in the superlattice. A large off‐resonant energy level alignment between two neighboring wells in the high field domain was observed. ©1995 American Institute of Physics.