Measurements are reported of the second‐harmonic distortion in 1.3‐&mgr;m InGaAsP distributed feedback lasers operating at different temperatures. A minimum of the second‐harmonic distortion exists at a particular bias current when the laser is operating at low temperature (10 °C). The minimum shifts to a higher bias current when the operating temperature is raised. At an even higher temperature, the minimum dissappears. A temperature‐dependent model of the second‐harmonic distortion, based on an equivalent circuit analysis, is presented to explain the experimental results.