The S4503 from ROHM Semiconductor is a MOSFET with Continous Drain Current 56 A, Drain Source Resistance 26 to 44 Milliohm, Drain Source Breakdown Voltage 750 V, Gate Source Voltage -4 to 21 V, Gate Source Threshold Voltage 2.8 to 4.8 V. Tags: Die. More details for S4503 can be seen below.