The MMST5551 from Galaxy Century Microelectronics 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 can be seen below.