Data are presented which indicate a modification of magnetic anisotropy in the MgO/CoFeB/Pd and MgO/CoFeB/Pt systems, using electric fields of order 500 MV m−1 (0.5 V nm−1) applied across a thermally grown SiO2 as a gate dielectric. The effect is most prominent at low temperature (12 K) and is manifested as a small change in coercivity. The sign of the effect depends on the choice of both capping layer and annealing temperature. The results suggest that both interfaces play a role in the appearance of perpendicular magnetic anisotropy in these thin-film stacks, and not just the interface with MgO.