This part is a kind of semiconductor called HER303.

Function of this product has 3.0A HIGH EFFICIENCY RECTIFIER.

Manufacturers : Diodes Incorporated

Image and pinout :

Some of the text within the PDF file :

HER301 - HER305 3.0A HIGH EFFICIENCY RECTIFIER Features · · · · · · · · Low Power Loss, High Efficiency Low Leakage Low Forward Voltage Drop High Current Capability High Speed Switching High Surge Current Rating High Reliability Plastic Material - UL Flammability Classification 94V-0 A B A D C Mechanical Data · · · · Case: Molded Plastic Terminals: Plated Axial Leads, Solderable per MIL-STD-202, Method 208 Polarity: Color Band Denotes Cathode Approx. Weight: 1.2 grams DO-201AD Dim A B C D Min 25.4 1.2 4.8 Max 9.5 1.3 5.2 All Dimensions in mm Maximum Ratings and Electrical Characteristics Ratings at 25° C ambient temperature unless otherwise specified. Single phase, half wave, 60Hz, resistive or inductive load. Characteristic Maximum Recurrent Peak Reverse Volt [ ... ]

HER303 PDF Datasheet Download