A further step in generalization of PF effect is got over, in considering the effect of a distribution of donors in energy, within the gap. Various laws of repartition are studied. Uniform distributions are first treated extensively. Computer simulations pointed out very conspicuous similarities with the one donor level case. Field-induced ionization is then derived for exponential distributions. An exponential law, given sometimes in literature, is analyzed throughout. Conditions of solvability of the basic differential equation are indicated. Moreover derivation and simulation are extended to a system of two uniform bands. Finally, an approximate method of resolution is proposed, when distributions of any shape are concerned.