This part is a kind of semiconductor called STR-4A60S.

Function of this product has Sensitive Gate Triacs.

Manufacturers : SemiWell Semiconductor

Image and pinout :

Some of the text within the PDF file :

SemiWell Semiconductor Sensitive Gate Triacs Features ◆ Repetitive Peak Off-State Voltage : 600V ◆ R.M.S On-State Current ( IT(RMS)= 4 A ) ◆ High Commutation dv/dt ◆ Sensitive Gate Triggering 4 Mode General Description This device is sensitive gate triac suitable for direct coupling to TTL, HTL, CMOS and application such as various logic functions, low power AC switching applications, such as fan speed, small light controllers and home appliance equipment. STR4A60S Symbol ○ 2.T2 ▼▲ ○ 3.Gate 1.T1 ○ TO-126 321 Absolute Maximum Ratings ( TJ = 25°C unless otherwise specified ) Symbol Parameter Condition VDRM IT(RMS) ITSM I2t Repetitive Peak Off-State Voltage R.M.S On-State Current Surge On-State Current I2t TC = 95 °C One Cycle, 50Hz/60Hz, [ ... ]

STR-4A60S PDF Datasheet Download