The QS8K21 from ROHM Semiconductor is a MOSFET with Continous Drain Current -4 to 4 A, Drain Source Resistance 38 to 75 Milliohm, Drain Source Breakdown Voltage 45 V, Gate Source Voltage -20 to 20 V, Gate Source Threshold Voltage 1 to 2.5 V. Tags: Surface Mount. More details for QS8K21 can be seen below.