Deep Ridge InGaAsP/InP Light Emitting Transistors (LET) with ~1.5 μm light emissions have been fabricated and characterized. In the deep ridge LETs, all the light emissions are from the intrinsic base area, which makes them more suitable for high speed direct modulation. A collector emitter voltage (V CE) dependent output power, which has been predicted numerically, is observed experimentally for the first time and may facilitate the use of LETs in optoelectronic integrations. A novel trend of self-heating related saturation of light power with base current is also observed, which is explained by the three port operation of the device. Further, an abnormal common-emitter current-voltage (I-V) characteristic of the deep ridge LETs is shown and is attributed to the non-radiative recombination centers at the ridge side walls. With the good quality of the quantum wells, laser operation at near room temperature is achieved in the deep ridge LET with 800 μm cavity length. With proper surface passivation techniques and device optimizations, performance of the deep ridge transistor based optoelectronic devices can be further enhanced greatly and ultra low power consumption which is highly desirable can be expected.