A model of gamma-ray flashes is presented. The model relies upon a horizont
al fractal lightning discharge, which generates the electromagnetic pulses
that pro duce the stochastic electron runaway discharge in the stratosphere
. The model computes the flux and energy spectrum of the gamma-rays generat
ed by the runaway discharge. The results of the computations are compared w
ith the GRO observations after including the gamma-rays attenuation in the
atmosphere.