Avalanche generation of minority carriers was studied under pulsed‐field conditions in thermally oxidized silicon surfaces. In the doping range between 5×1016and 1×1018cm−3avalanche breakdown voltages and fields are in agreement with step‐junction results. For lower doping, breakdown voltages are below the expected values. Avalanche light‐emission observations revealed this effect to be due to field concentration at the contact edges. In the higher doping range between 1018and 1019cm−3minority carriers are produced by Zener tunneling. Band bending for tunneling is 1.1 V, independent of doping.