At SiO2 films thermally grown on phosphorus doped polycrystalline silicon hopping currents according to j = A exp ( B/F1/4) are observed in the field range of 5 × 105 to 2.5 × 106 V cm−1. From the j−F characteristics of films thicker than 50 nm grown in wet nitrogen the density of deep traps is calculated to be (2.75 ± 1.5) × 1018 cm−3 within an energy band at the Fermi level which has a width at least of 0.065 eV. In films grown in dry oxygen the according values are somewhat lower. At thinner films the trap density strongly increases with decreasing film thickness to values above 1019 cm−3. The results well agree with the assumption of channel‐like regions of enlarged trap density acting as hopping paths. The calculated trap densities then are concerned with these paths of hopping conduction which are embedded in larger areas of lower trap density.