This part is a kind of semiconductor called BT137.

Function of this product has TRIAC.

Manufacturers : UTC

Image and pinout :

Some of the text within the PDF file :

UTC BT137 TRIAC TRIACS DESCRIPTION Passivated triacs in a plastic envelope, intended for use in applications requiring high bidirectional transient and blocking voltage capability and high thermal cycling performance. Typical applications include motor control, industrial and domestic lighting, heating voltages and static switching. SYMBOL MT2 1 TO-220 G MT1 1:MT1 2:MT2 3:GATE ABSOLUTE MAXIMUM RATINGS PARAMETER SYMBOL RATINGS UNIT Repetitive Peak Off State Voltage BT137-600 BT137-800 VDRM 600 800* -600 -800 V RMS On-state Current (Full sine wave; Tmb≤102°C) IT(RMS) 8 A Non-Repetitive Peak. On-State Current (Full sine wave; Tj=25°C prior to surge) t=20ms ITSM 65 A t=16.7ms 71 I2t For Fusing t=10ms I2t 21 A2s Repetitive Rate of Rise of On-state Current af [ ... ]

BT137 PDF Datasheet Download