We report the first direct observation of the self-imaging effect in active multimode-interference semiconductor laser diodes (MMI-SLDs). Interference patterns inside laser diode waveguides were obtained by using the electroluminescence (EL) method. To the best of our knowledge, this result is the first direct observation of the self-imaging effect in self-photon-emitting active waveguides such as laser diodes. The observed EL pattern confirms the adequateness of the design of the higher light output-aimed MMI-SLDs.