Current sensing in power semiconductors involves sensing of over-current in order to protect the device from harsh conditions. This technique is one of the most important functions in stabilizing power semiconductor device modules. The sense FET is very efficient method with low power consumption, fast sensing speed and accuracy. In this paper, we have analyzed the characteristics of proposed sense FET and optimized its electrical characteristics to apply conventional 450 V power MOSFET by numerical and simulation analysis. The proposed sense FET has the n-drift doping concentration $1.5{ imes}10^{14}cm^{-3}$, size of $600{um}m^2$ with $4.5;{Omega}$, and off-state leakage current below $50{mu}A$. We offer the layout of the proposed sense FET to process actually. The offerd design and optimization methods are meaningful, which the methods can be applied to the power devices having various breakdown voltages for protection.