The STW21N90K5 from STMicroelectronics is a MOSFET with Continous Drain Current 18.5 A, Drain Source Resistance 250 to 299 Milliohm, Drain Source Breakdown Voltage 900 V, Gate Source Voltage -30 to 30 V, Gate Source Threshold Voltage 3 to 5 V. Tags: Through Hole. More details for STW21N90K5 can be seen below.