In this work, TCAD simulation has been applied to study the Power U- shape metal-oxide-semiconductor field- effect transistor (P-island Power UMOSFET) with p-type islands to determine its sensitivity to Single Event Burnout (SEB). In the drift area, the p-type buried islands suppress the strong electric field at the bottom of the trench and prevent SEB. For the appropriate device design, the effect of doping concentration, thickness, length, and position of the p-islands on the breakdown voltage and the threshold voltage is studied. Using optimized parameters for the P-island, the hardened PI-UMOS obtains unchanged electrical characteristics from the standard UMOSFET. The outcome of the SEB simulations shows that the electrical field in the hardened structure is decreased by 60.12 relative to a standard structure and that the survivability of the SEB has also improved substantially by about 30.1. Hence, Power UMOSFET with P-islands offers high SEB survivability for space and atmospheric applications. © 2020 IEEE.