In a method of manufacturing a magnetoresistive random access memory, a memory structure may be formed on a substrate. The memory structure may include a lower electrode, a magnetic tunnel junction (MTJ) structure, and an upper electrode sequentially stacked. A protection layer including silicon nitride may be formed to cover a surface of the memory structure. The protection layer may be formed by a chemical vapor deposition process using plasma and introducing deposition gases including a silicon source gas, a nitrogen source gas containing no hydrogen and a dissociation gas. Damages of the MTJ structure may be decreased during forming the protection layer. Thus, the MRAM may have improved characteristics.