Monte Carlo simulations of electronic high‐field transport in Si are performed. Contrary to previous treatments of impact ionization, we do not employ the ordinary Keldysh formula [Sov. Phys. JETP21, 1135 (1965)] with a soft threshold, but rather a new expression, which is an explicit function of the wave vector of the initiating electron, is used. The calculation results of drift velocity, ionization coefficient, and quantum yield show excellent agreement with the experimental data. Our results strongly substantiate the idea that the ionization threshold is basically hard even in Si in the sense that the electrons rapidly ionize when they approach the threshold energies and that the softness of the ionization threshold is introduced through the wave vector dependence of the threshold energies.