This part is a kind of semiconductor called 4N40.

Function of this product has N-CHANNEL POWER MOSFET.

Manufacturers : Unisonic Technologies

Image and pinout :

Some of the text within the PDF file :

UNISONIC TECHNOLOGIES CO., LTD 4N40 4A, 400V N-CHANNEL POWER MOSFET  DESCRIPTION The UTC 4N40 is an N-channel mode power MOSFET using UTC’ s advanced technology to provide customers with planar stripe and DMOS technology. This technology specializes in allowing a minimum on-state resistance and superior switching performance. It also can withstand high energy pulse in the avalanche and commutation mode. The UTC 4N40 is universally applied in electronic lamp ballast based on half bridge topology and high efficient switched mode power supply.  FEATURES * High switching speed * RDS(ON)<1.5Ω @ VGS=10V, ID=2A * 100% avalanche tested  SYMBOL 2.Drain Power MOSFET 1.Gate 3.Source  ORDERING INFORMATION Note: Ordering Number Lead Free Halogen Free 4N40L-TA3-T 4N40G-TA3- [ ... ]

4N40 PDF Datasheet Download