The formation of dark spot defects (DSDs) in InP/InGaAsP aged light emitting diodes has been investigated by spatially resolved cathodoluminescence, transmission electron microscopy and Rutherford backscattering. It is shown that DSDs are caused by the migration of Au from the p-contact. This migration occurs during device processing and aging. As a consequence, Au-In intermetallics and inclusions associated with glide dislocations and multiple faults form, respectively, within the contact and p-InP confining layers. These features are responsible for dark spot contrast observed in electroluminescent images.