The capability of producing electronically induced modifications in ultrathin (∼20 nm) light‐emitting porous silicon (PS) films by use of a scanning tunneling microscope (STM) operated in a high‐vacuum environment is demonstrated. Upon increasing the tunnel current to 2 nA and the tunnel voltage beyond a threshold value of ∼7 V, structures 20–50 nm in width can be created to any desired pattern. These nanopatterns are stable at least for four days at room temperature. Experiments with both voltage polarities but equal power densities reveal that these structures can only be induced by directing the intense electron beam provided by the STM tip towards the sample surface, excluding pure thermal effects for the layer modifying process. These observations can be well explained by a model which includes a local increase in the density of defect states in deep‐layer regions of the PS layer, which might be accompanied by a local quenching of the photo‐ or electroluminescence activity. ©1996 American Institute of Physics.