This part is a kind of semiconductor called C106D.

Function of this product has Sensitive Gate Silicon Controlled Rectifiers.

Manufacturers : ON Semiconductor

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Some of the text within the PDF file :

C106 Series Preferred Devices Sensitive Gate Silicon Controlled Rectifiers Reverse Blocking Thyristors Glassivated PNPN devices designed for high volume consumer applications such as temperature, light, and speed control; process and remote control, and warning systems where reliability of operation is important. • Glassivated Surface for Reliability and Uniformity • Power Rated at Economical Prices • Practical Level Triggering and Holding Characteristics • Flat, Rugged, Thermopad Construction for Low Thermal Resistance, High Heat Dissipation and Durability • Sensitive Gate Triggering • Device Marking: Device Type, e.g., C106B, Date Code MAXIMUM RATINGS (TJ = 25°C unless otherwise noted) Rating Peak Repetitive Off–State Voltage (Note 1) (Sine Wave, 50–60 Hz, RGK = 1 kΩ, [ ... ]

C106D PDF Datasheet Download