The STB20NM50 from STMicroelectronics is a MOSFET with Continous Drain Current 20 A, Drain Source Resistance 200 to 250 Milliohm, Drain Source Breakdown Voltage 500 V, Gate Source Voltage -30 to 30 V, Gate Source Threshold Voltage 3 to 5 V. Tags: Surface Mount. More details for STB20NM50 can be seen below.