This part is a kind of semiconductor called MCR100-6.

Function of this product has PLASTIC SILICON CONTROLLED RECTIFIERS(PNPN devices designed for high volume).

Manufacturers : Unisonic Technologies

Image and pinout :

Some of the text within the PDF file :

UNISONIC TECHNOLOGIES CO., LTD MCR100 SCR SENSITIVE GATE SILICON CONTROLLED RECTIFIERS REVERSE BLOCKING THYRISTORS 3 21 SOT-23 1 SOT-223  DESCRIPTION PNPN devices designed for high volume, line-powered consumer applications such as relay and lamp drivers, small motor controls, gate drivers for larger thyristors, and sensing and detection circuits.  FEATURES * Sensitive gate allows triggering by micro controllers and other logic circuits * Blocking voltage to 600V * On-state current rating of 0.8A RMS at 80C * High surge current capability – 10A * Minimum and maximum values of IGT, VGT and IH specified for ease of design * Immunity to dV/dt – 20V/μsec minimum at 110C * Glass-passivated surface for reliability and uniformity  ORDERING INFORMATION Ordering Number [ ... ]

MCR100-6 PDF Datasheet Download