The SSM3K123TU from Toshiba is a MOSFET with Continous Drain Current 4.2 A, Drain Source Resistance 19 to 66 Milliohm, Drain Source Breakdown Voltage 20 V, Gate Source Voltage -10 to 10 V, Gate Source Threshold Voltage 0.35 to 1 V. Tags: Surface Mount. More details for SSM3K123TU can be seen below.