In GaAs‐AlGaAs single and multiple quantum‐well (SQW and MQW) ridge lasers, grown by molecular beam epitaxy, the temperature dependence of the threshold current, expressed by the characteristic temperature T0, is investigated as a function of the cavity length (L) at temperatures between 20 °C and 93 °C. SQW lasers, in contrast to MQWs, show at room temperature a strong decrease in T0 from 250 K to about 100 K when the length is reduced from 400 to 200 μm. We found that by further reducing L to about 130 μm, a strong increase in T0 up to 250 K occurs and T0 decreases again to 80 K for 60 μm SQW lasers. This T0 behavior in SQW lasers is directly correlated to the gain saturation of the n=1 transition and the switch of the laser emission to the n=2 transition. In MQW lasers, T0 is constant at all cavity lengths, even at high temperatures, indicating that no gain saturation occurs.