This part is a kind of semiconductor called AP99T03GS-HF-3.

Function of this product has N-CHANNEL ENHANCEMENT MODE POWER MOSFET.

Manufacturers : Advanced Power Electronics

Image and pinout :

Some of the text within the PDF file :

Advanced Power Electronics Corp. AP99T03GP/R/S-HF-3 N-channel Enhancement-mode Power MOSFET Simple Drive Requirement Very Low On-resistance Fast Switching Performance RoHS-compliant, halogen-free G S D BV DSS RDS(ON) ID 30V 2.5mΩ 200A Description Advanced Power MOSFETs from APEC provide the designer with the best combination of fast switching, low on-resistance and cost-effectiveness. The AP99T03GS-HF-3 is in the TO-263 package, which is widely used for commercial and industrial surface-mount applications, and is well suited for low voltage applications such as DC/DC converters. The AP99T03GP-HF-3 is in the TO-220 through-hole package which is used where a small PCB footprint or an attached heatsink is required. Also available in the TO-262 surface mount package (AP99T03GR-HF-3) whi [ ... ]

AP99T03GS-HF-3 PDF Datasheet Download