This part is a kind of semiconductor called HER303.

Function of this product has 3A High Efficiency Diodes.

Manufacturers : Leshan Radio Company

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Some of the text within the PDF file :

LESHAN RADIO COMPANY, LTD. HER301 thru HER308 1.Feature & Dimensions High Efficiency Rectifiers * Plastic package has Underwriters Laboratory Flammability Classification 94V-0 * High temperature metallurgically bonded construction Reverse Voltage 50 to 1000V Forward Current 3.0A * Deffused junction * Capable of meeting environmental standards of MIL-S-19500 * 3.0 A operation at TA=55°C with no thermal runaway * For use in high frequency rectifier circuits * Fast switching for high efficiency * Typical IR less than 1.0µA * High temperature soldering guaranteed: 260°C/10 seconds * 0.375" (9.5mm) lead length, 5 lbs. (2.3kg) tension 2.Mechanical Data Case: JEDEC DO-201AD, molded plastic body Terminals: Plated axial leads, solderable per MIL-STD-750, Method 2026 Polarity: Col [ ... ]

HER303 PDF Datasheet Download