The ratio of total electron yield and stopping power (specific yield) is investigated. Both quantities are calculated using the same basic assumptions concerning the different interaction processes. We have taken into account all known excitation and scattering processes within the calculation of the electron yield. For proton impact on aluminum we obtain a decrease of the specific yield with increasing proton energy. This is in contrast to the observed independence of the specific yield of the impact energy but in accordance with the observed behaviour for heavier projectiles.