I'm trying to identifiy this component. I assume that it must be some kind of mosfet or bjt. Can someone point me to a Manufacturer Part number or datasheet?
As mentioned in the comments, this will be a simple Thyristor in a DPAK type package.
The BT151S-500 from WeEn-Semi (now part of NXP) matches the package (SOT428/DPAK), and also the partial part number (151S5).