This part is a kind of semiconductor called STTH6003.

Function of this product has HIGH FREQUENCY SECONDARY RECTIFIER.

Manufacturers : ST Microelectronics

Image and pinout :

Some of the text within the PDF file :

® STTH6003TV/CW HIGH FREQUENCY SECONDARY RECTIFIER MAJOR PRODUCT CHARACTERISTICS IF(AV) VRRM VF (max) trr (max) FEATURES AND BENEFITS COMBINES HIGHEST RECOVERY AND VOLTAGE PERFORMANCE ULTRA-FAST, SOFT AND NOISE-FREE RECOVERY INSULATED PACKAGE: ISOTOP Insulation voltage: 2500 VRMS Capacitance: < 45 pF LOW INDUCTANCE AND LOW CAPACITANCE ALLOW SIMPLIFIED LAYOUT DESCRIPTION Dual rectifiers suited for Switch Mode Power Supply and high frequency DC to DC converters. Packaged either in ISOTOP or in TO-247, this device is intended for use in low voltage, high ABSOLUTE RATINGS (limiting values, per diode) Symbol VRRM IF(RMS) IF(RMS) IF(AV) Parameter Repetitive peak reverse voltage RMS forward current RMS forward current Average forward current ISOTOP TO-247 IFSM IRSM Tstg Tj Surge non repetitive [ ... ]

STTH6003 PDF Datasheet Download