Space-related electronics contain different types of oxide isolations which are the crucial factor resulting in device degradation and failure. Previous studies show that the local oxidation of silicon (LOCOS) isolation Silicon-germanium heterojunction bipolar transistor (SiGe HBT) experience more significantly low dose rate sensitivity than that of shallow trench (STI) isolation SiGe HBTs and behave a "true" dose rate effect. In our work, the electron-hole pairs (EHPs) generation, holes trapped and protons transport inside oxide are simulated in LOCOS and STI isolation SiGe HBTs to explanation the different response t enhanced low dose rate sensitivity (ELDRS). The simulation results show that LOCOS oxide has a larger generation of EHPs than that of STI oxide leading to more surviving holes and protons release within oxide.