We present a study of the transport characteristics of electrons through abrupt GaAs–Ga1−xAlxAs–GaAs(100) double heterojunctions. The theoretical apparatus uses complex‐k‐band structures in the tight‐binding approximation and transfer matrices. States on each side of the Ga1−xAlxAs central barrier are expanded in terms of a complex‐k‐bulk state basis so as to provide a description of the wave function at the GaAs–Ga1−xAlxAs(100) interface. We treat the case where the incoming state in GaAs is derived from near the conduction band Γ point. Transmission through the Ga1−xAlxAs barrier is either tunneling or propagating depending on the nature of the Bloch states available for strong coupling in the alloy. States derived from the same extremum of the conduction band appear to couple strongly to each other across the GaAs–Ga1−xAlxAs interface. Transport characteristics of incoming states derived from near the conduction band Γ point are examined as a function of the energy of the incoming state, thickness of the Ga1−xAlxAs barrier, and alloy compositionx. Transmission through the Ga1−xAlxAs barrier is either tunneling or propagating, depending on the nature of the Bloch states available for strong coupling in the alloy.