This part is a kind of semiconductor called 2SD1257A.

Function of this product has Silicon NPN epitaxial planar type(For power switching).

Manufacturers : Panasonic Semiconductor

Image and pinout :

Some of the text within the PDF file :

Power Transistors 2SD1257, 2SD1257A Silicon NPN epitaxial planar type For power switching Complementary to 2SB934 10.0±0.3 8.5±0.2 6.0±0.5 3.4±0.3 Unit: mm 1.0±0.1 s Features q q q q Low collector to emitter saturation voltage VCE(sat) Satisfactory linearity of foward current transfer ratio hFE Large collector current IC N type package enabling direct soldering of the radiating fin to the printed circuit board, etc. of small electronic equipment. (TC=25˚C) Ratings 130 150 80 100 7 15 7 40 1.3 150 –55 to +150 Unit V 1.5±0.1 1.5max. 1.1max. 10.5min. 2.0 0.8±0.1 0.5max. 2.54±0.3 5.08±0.5 1 2 3 s Absolute Maximum Ratings Parameter Collector to base voltage Collector to 2SD1257 2SD1257A 2SD1257 Symbol VCBO VCEO VEBO ICP IC PC Tj Tstg 1:Base 2:Collector 3:Emitter N Type [ ... ]

2SD1257A PDF Datasheet Download