A semiconductor device including a substrate; a lower electrode on the substrate; a magnetic tunnel junction structure on the lower electrode, the magnetic tunnel junction structure including a pinned layer, a tunnel barrier layer, and a free layer which are sequentially stacked; an upper electrode on the magnetic tunnel junction structure; and an oxidation control layer between the free layer and the upper electrode, the oxidation control layer including at least one filter layer and at least one oxide layer, wherein the at least one filter layer includes MoCoFe.