This part is a kind of semiconductor called K643.
Function of this product has 2SK643.
Manufacturers : Toshiba Semiconductor
Image and pinout :

Some of the text within the PDF file :
www.DataSheet.co.kr Datasheet pdf - http://www.net/ www.DataSheet.co.kr Datasheet pdf - http://www.net/ [ ... ]
K643 PDF Datasheet Download
