Irreversible formation of a network of linear defects has been observed for images showing recombination luminescence from injection diodes in hexagonal silicon carbide. The defects are related to dislocations that are initially formed as a result of thermal stress near the tip of the contact probe and subsequently propagate through the diode area. The dislocation network appears in the images of the electroluminescence as bright-line defects, in contrast to the well-known dark-line defects due to degradation of gallium–arsenide-based light-emitting devices. Higher forward currents are found to promote the dislocation growth. ©1997 American Institute of Physics.