A new method of electro‐optic sampling field transients, using above‐band‐gap optical probes in reflection, is analyzed theoretically and experimentally demonstrated to be within a factor of 2 as sensitive as electro‐optic sampling in transmission. The technique is ideally suited to the study of interfaces due to the surface selective nature of the evanescent field probe. Studies of the dynamics of photogenerated electron‐hole pair separation in surface‐space‐charge fields at GaAs(100)/oxide interfaces show that the hole carrier transit time is faster than 500 fs. Using longitudinal electro‐optic sampling beam geometries, this technique has an intrinsic resolution of 50 fs.