A new method is presented to measure the thermal resistance (R/sub th/) of semiconductor lasers. We show that knowing the applied junction voltage, the electrical series resistance and the experimental I/sub th/ vs. T characteristic in pulsed operation is possible to evaluate R/sub th/. The key advantage of the method is that it avoids the measurement in continuous-wave (CW) operation. In particular we consider the case when I/sub th/ versus T characteristics exhibit kinks. To verify our method, CdZnSe, InGaAs, GaN and AlGaAs lasers were analyzed. We show that values obtained in this way agree quite well with the values measured by traditional methods.