The surface potential of GaAs is strongly modified in the presence of a high‐energy electron beam due to the creation of electron‐hole pairs in the depletion region and the subsequent drift of the holes to the surface where they neutralize surface states. This effect is modeled in terms of a parameter K=A∗T2/Ib(dE/dz)η, where Ib is the beam current density, A∗ is the effective Richardson constant, dE/dz is the beam energy loss per unit length, and η−1 is the average energy required to create an electron‐hole pair. For the sample studied here, an 0.25‐μm layer with n≂3×1017 cm−3, we obtain a value K≂(7.5±0.8)×104 cm at T=296 K and Ib=0.33 μA/cm2, which gives A∗≂0.44 A/cm2 K2. Although this value of A∗ is much lower than the theoretical estimate of 8 A/cm2 K2, it is in good agreement with other recent results.