The STPS8L30BY-TR is a 30 V, 8 A Schottky rectifier in a DPAK surface-mount package. The 8 A average rating is the continuous forward current the part can carry with the tab soldered to adequate copper area. The 490 mV forward drop at 8 A drives conduction loss.
Junction temperature and the thermal budget
That 150°C ceiling is the hard limit — push past it and the leakage current climbs fast, especially on a 30 V Schottky where reverse leakage at rated Vr is already 1 mA at 25°C. In a 85°C ambient with the diode carrying 6 A, the junction will sit around 110-120°C depending on the board's thermal pad. That's fine for industrial or automotive under-hood use, but if the board is sealed in a hot enclosure, you'll want to measure the case temperature in the actual build.
The DPAK (TO-252) footprint is standard — the tab is the cathode, and the two anode pins are tied together internally.