Magnetic random access memory (MRAM) with a synthetic ferrimagnetic (SF) pinned layer has been investigated experimentally and theoretically. The SF pinned layer offers the higher thermal stability due to its even higher anisotropy and larger total thickness. A smaller aspect ratio cell with single domain state, less switching field dependence on the cell size, and lower switching field can be achieved in the SF structure than that in the conventional structure because of the thinner effective thickness. The experimental results show that high heat tolerance can also be achieved in the SF MRAM structure.