It is shown that the existence of nonabrupt interfaces modify electric field effects on the electron transmission through a GaAs/AlxGa1-xAs double-barrier. When the applied electric intensity is 25 kV/cm, and the abrupt well and barriers are 100 Å wide, interfaces as thin as two GaAs lattice parameters are responsible for shifts at least of 10 meV in the electron tunneling resonance energies. The type of interface potential and electron effective mass description changes significantly theoretical results related to the electric field influence on the electron transmission properties.