The BT258S-800R from WeEN Semiconductors is a Silicon Controlled Rectifier with Breakover Voltage 800 V, Breakover Current 75 A, Gate Trigger Voltage 0.1 to 1 V, Gate Trigger Current 0.0002 A, Temperature Operating Range -40 to 150 Degree C. Tags: Surface Mount. More details for BT258S-800R can be seen below.