The photo-bidirectional negative resistance transistor (PBNRT) is a novel "S" type photoelectric negative resistance device.Its photoelectric negative resistance characteristics were investigated both by experiment and numerical simulation and its equivalent circuit is proposed.PBNRT has photo-controlled current switching effect in the optical and electric mixed operating mode

and its "S" negative resistance characteristics can be modulated by two different controlled ways

using light and controlled voltage respectively.The simulated and experimental results both indicate that on increasing optical intensity

sustaining voltage almost remains unchanged and snapback voltage decreases

thus reducing the negative resistance voltage range; while as controlled voltage increases

sustaining voltage and snapback voltage both increase accordingly

and output negative resistance characteristic curve shifts right.All the properties mentioned above make it suitable for photoelectric switching

photo-controlled oscillation and photoelectric detector.