We report measurements of the temperature dependence of the threshold current of GaAs, 1.3‐&mgr;m InGaAsP, and 1.5‐&mgr;m InGaAsP double heterostructure lasers using short electrical pulses.T0∼200 K is observed for all the lasers. These highT0values show that the carrier density at threshold does not increase rapidly with increasing temperature in any of the lasers studied and thus the observed low cwT0of InGaAsP lasers is primarily due to a decrease of the carrier lifetime at threshold with increasing temperature.