Our purpose is to seek that the reachable set of the semilinear system $frac{d}{dt}x(t){;}={;}Ax(t){;}+{;}f(t,x(t)){;}+{;}Bu(t)$ is equivalent to that of its corresponding to linear system (the case where f=0).Under the assumption that the system of generalized eigenspaces of A is complete, we will show that the reachable set corresponding to the linear system is independent of t in case A generates $C_0-semigroup$. An illustrative example for retarded system with time delay is given in the last section.