We prove that both local and global Łojasiewicz exponent of a continuous overdetermined semialgebraic mapping F : X → Rᵐ on a closed semialgebraic set X ⊂ Rⁿ (i.e. m > dimX) are equal to the Łojasiewicz exponent of the composition L ₒ F : X → Rᵏ for the generic linear mapping L : Rᵐ → Rᵏ, where k = dimX