We conducted a detailed study of the interlayer exchange coupling (JEX) dependence of thermal stability properties of magnetic tunnel junctions (MTJs) with synthetic antiferromagnetic (Syn-AF) free layers. The thermal stability properties were investigated using the junction magnetoresistance of current-perpendicular MTJ devices with a word line as probes. The observed sweep-rate-dependent coercivities were analyzed using the Sharrock formula. The results confirmed the existence of strong JEX dependence on thermal stability parameters (Ku VkT) in Syn-AF free layers. The values of Ku VkT for MTJs with Syn-AF free layers decreased with a decrease in the strength of JEX, and the increase in the effective volume of the Syn-AF free layer disappeared at JEX ≤0.52 erg cm2. The Syn-AF free layer with JEX >0.52 erg cm2 is relevant for high-density spin electronic nanodevices with a low aspect ratio.