A semiconductor device is disclosed including one or more semiconductor dies mounted on substrate. Each semiconductor die may be formed with a ferromagnetic layer on a lower, inactive surface of the semiconductor die. The ferromagnetic layer pulls the semiconductor dies down against each other and the substrate during fabrication to prevent warping of the dies. The ferromagnetic layer also balances out a mismatch of coefficients of thermal expansion between layers of the dies, thus further preventing warping of the dies.