We demonstrate a novel technique for estimating carrier leakage current in double heterostructure lasers. This utilizes the dependence of the carrier leakage motion on the high magnetic field directions. The carrier leakage current near threshold in GaInAsP‐InP lasers is estimated as a function of temperature from −25 to 65 °C. The result indicates that theT0value is improved from 58 to about 77 °C by suppressing the leakage current.