The probability B that a secondary electron internally excited in an insulator escapes upon reaching the surface is extracted from experiment and discussed theoretically for the first time. It is shown that B=2.5δmϵ/E0m, where ϵ is the electron‐hole‐pair creation energy and δm and E0m are the maximum secondary yield and the primary energy of maximum yield, respectively. It is also shown that ϵ=2.8Eg, where Eg is the insulator band gap. Values of B are extracted from secondary‐electron‐emission data for many semiconductors. A simple theory relating B to χ/Eg, the ratio of the electron affinity and the band gap is developed and shown to define an upper bound for the experimental data. The free‐particle approximation adequately describes these hot‐ (energies ≳1 eV) electron phenomena.
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