  Electron transmission through semiconductor superlattices is studied with
transfer matrix method and resonance theory. The formation of electron
band-pass transmission is ascribed to the coupling of different modes in those
semiconductor superlattices with the symmetric unit cell. Upon Fabry-P\'erot
resonance condition, Bloch modes and two other resonant modes are identified to
be related to the nature of the superlattice and its unit cell, respectively.
The bands related to the unit cell and the superlattice overlap spontaneously
in the tunneling region due to the shared wells, and the coupling of perfectly
resonances results in the band-pass tunneling. Our findings provide a promising
way to study electronic systems with more complicated superlattices or even
optical systems with photonic crystals.
