Determination of reliability performance over time requires an accurate understanding of device junction temperature, not only in customer use condition, but also during production test and burn-in. Through carefully designed and executed LIV (L=Light, I=current, V=Voltage) measurements and a modeling framework where optical power, thermal and electrical device parameters are interrelated, the laser diode junction temperature, as confirmed by wavelength shift measurements, is obtained via regression of a non-linear self-consistent equation.  Modeled parameters include both threshold current and slope efficiency junction linear temperature dependence coefficients/constants, as well as a thermal impedance factor.