The mirror‐substrate method was used for measuring the penetration depth of 0.5–3‐keV electrons in solid hydrogen and deuterium. The penetration depth was found to be 0.53×1018E1.72molecules/cm2with the energy given in keV. There was satisfactory agreement with other data. The measurements also showed that the escape depth for true secondary electrons from solid deuterium is less than 50 A˚, which agrees well with the small values for the secondary‐electron‐emission coefficient found for solid deuterium. Results were furthermore obtained for the electron‐reflection coefficient for the gold substrate, i.e., the number of electrons that are reflected with high energies. The electron‐reflection coefficient agrees well with other results, both with respect to magnitude and energy dependence.