This is one of the semiconductor types. This part name is STK58C308.
This product has Tiuch Dimmer functions.
Manufacturers of product is Syntek Semiconductor.
Image and pinout :
STK58C308 PDF Datasheet
Some of the text files within the PDF file
It is a selectable 3-section or switch function dimmer. The dimmer can keep the original brightness in the absence of power within 1 second and return to OFF state if power failure exceeds 1 second. [ … ]
Please refer to the file for details.