The MMST5551-TP from Micro Commercial Components is a Bipolar Junction Transistor with Emitter Base Voltage 6 V, Base Emitter Saturation Voltage 1 V, Emitter Cut off Current 50 nA, Collector Base Voltage 180 V, Collector Cut off Current 50 nA. Tags: Surface Mount, NPN Transistor. More details for MMST5551-TP can be seen below.