  Probabilistic interpretation of transition from the dispersive transport
regime to the quasi-Gaussian one in disordered semiconductors is given in terms
of truncated Levy distributions. Corresponding transport equations with
fractional order derivatives are derived. We discuss physical causes leading to
truncated waiting time distributions in the process and describe influence of
truncation on carrier packet form, transient current curves and frequency
dependence of conductivity. Theoretical results are in a good agreement with
experimental facts.
