  We introduce and analyze the properties of dynamical Franz-Keldysh effect,
i.e. the change of density-of-states, or absorption spectra, of semiconductors
under the influence of {\it time-dependent} electric fields. In the case of a
harmonic time-dependence, we predict the occurence of significant fine
structure, both below and above the zero-field band-gap, which should be
experimentally observable.
