This part is a kind of semiconductor called BAV21WS.

Function of this product has SURFACE MOUNT FAST SWITCHING DIODE.

Manufacturers : Diodes Incorporated

Image and pinout :

Some of the text within the PDF file :

Features  Fast Switching Speed  Surface Mount Package Ideally Suited for Automated Insertion  For General Purpose Switching Applications  High Conductance  Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)  Halogen and Antimony Free. “Green” Device (Note 3)  Qualified to AEC-Q101 Standards for High Reliability BAV19WS - BAV21WS SURFACE MOUNT FAST SWITCHING DIODE Mechanical Data  Case: SOD323  Case Material: Molded Plastic, “Green” Molding Compound. UL Flammability Classification Rating 94V-0  Moisture Sensitivity: Level 1 per J-STD-020  Terminal Connections: Cathode Band, See Page 2  Terminals: Matte Tin Finish Annealed over Alloy 42 Leadframe. Solderable per MIL-STD-202, Method 208  Weight: 0.004 grams (Approximate) SOD323 Top View O [ ... ]

BAV21WS PDF Datasheet Download