A method for determining the geometrical surface trap structure of highly insulating polymer films is presented. We compare ’’open‐circuit’’ thermally‐stimulated current measurements of corona and electron‐beam‐charged foils. We present the results for three different polymers: polyfluoroethylenepropylene [Teflon (FEP)], polyethyleneterephthalate [Mylar (PET)], and Polyethylene (PE). For Teflon one observes that the surface traps are energetically shallower than the bulk traps, for Mylar no separate surface traps exist whereas for polyethylene the situation is opposite to Teflon. The spatial resolution of the method is 0.5 &mgr;m.