The STD3N40K3 from STMicroelectronics is a MOSFET with Continous Drain Current 2 A, Drain Source Resistance 2700 to 3400 Milliohm, Drain Source Breakdown Voltage 400 V, Gate Source Voltage -30 to 30 V, Gate Source Threshold Voltage 3 to 4.5 V. Tags: Surface Mount. More details for STD3N40K3 can be seen below.