A scanning tunneling microscope (STM) is used to locally modifyp‐njunctions on a scale of a few tens of nanometers. Thep‐njunction is composed of a phosphorus‐doped, hydrogenated amorphous Si [a‐Si:H(P)] layer deposited on heavily dopedp‐type crystalline Si(111). Under conditions of high current densities, with thep‐njunction biased in forward direction, thea‐Si:H layer is structurally changed leading to a decrease of the junction barrier height. The resulting exponential increase of hole injection into the modified amorphous layer leads to electronically active structures. They are detected by STM owing to their differing electronic properties.