A blue frequency shift in a distributed‐feedback laser diode (DFB‐LD) induced by light injection is described. It is observed in an experiment that the lasing wavelength shifts toward the shorter wavelength and the carrier number increases when external light is injected into a DFB‐LD in a particular condition. AnFmatrix analysis shows a similar behavior, where spatial distribution of the carrier density induced by the external light is taken into account. ©1995 American Institute of Physics.