Due to the submicron size of crystallographic defects, characterization of dislocations has been done. mostly by electron microscopy techniques. Transmission electron microscopy has generated invaluable structural information at the atomic scale. However, the influence of these electrically active defects on carrier transport can only be learned from lower resolution (∼ 1 μm) techniques such as electron beam induced current (EBIC) and photocurrent measurements. Near-field scanning optical microscopy (NSOM) is a novel optical technique that circumvents the diffraction limit. In this talk, we will present the application of NSOM to perform near-field photocurrent (NPC) measurements on strain-relaxed GeSi films on Si substrates to study the electrical activity of individual threading dislocations. Photoexcited carriers are generated locally by NSOM light and are collected by the builtin p-n junctions in the sample resulting in an external photocurrent. As the tip moves across the sample, topographic and NPC images were acquired simultaneously.