The Si4559ADY from Vishay is a MOSFET with Continous Drain Current 5.3 A, Drain Source Resistance 46 to 150 milliohm, Drain Source Breakdown Voltage 60 V, Gate Source Voltage -20 to 20 V, Gate Source Threshold Voltage -1 to 3 V. Tags: Surface Mount. More details for Si4559ADY can be seen below.