  We propose a novel type of ionization front in layered semiconductor
structures. The propagation is due to the interplay of band-to-band tunneling
and impact ionization. Our numerical simulations show that the front can be
triggered when an extremely sharp voltage ramp ($\sim 10 {\rm kV/ns}$) is
applied in reverse direction to a Si $p^+-n-n^+-$structure that is connected in
series with an external load. The triggering occurs after a delay of 0.7 to 0.8
ns. The maximal electrical field at the front edge exceeds $10^6 {\rm V/cm}$.
The front velocity $v_f$ is 40 times faster than the saturated drift velocity
$v_s$. The front passes through the $n-$base with a thickness of $100 {\mu m}$
within approximately 30 ps, filling it with dense electron-hole plasma. This
passage is accompanied by a voltage drop from 8 kV to dozens of volts. In this
way a voltage pulse with a ramp up to $500 {\rm kV/ns}$ can be applied to the
load. The possibility to form a kilovolt pulse with such a voltage rise rate
sets new frontiers in pulse power electronics.
