The I-V characteristics of InP/AlGaInP quantum dot laser diodes with different cavity lengths were measured at different temperatures (77–400K). From the forward bias I-V characteristics, the laser diode electrical parameters, as the ideality factor (n), the reverse saturation current (Js), and series resistance (Rs) were extracted. The values of the ideality factor depend slightly on the temperature in the temperature range above 150 K while it increases as the temperature decreases below this value. It is noticed that the increase of n for a longer cavity is greater. This may be attributed to the freezing out of the mobile charge carriers in the n and p emitters of the diode. Conversely, Js increases with the temperature. It follows almost an exponential increase with temperature most probably because of the thermal generation of electron-hole pairs across the energy gap of the material. Rs behaves in a similar way where it is almost constant at T > 150 K. It appreciably increases with further lowering the temperature with the shortest cavity having the greatest increase. Rs decreases as the cavity length increases. This may again be attributed to the freeze out or the mobile charge carriers in the end emitter regions of the device. For our best knowledge such results are reported for the first time for these diodes.