A manganese telluride (MnTe) compound is an interesting polymorphic semiconductor with physical properties differing greatly among various polymorphs. In this study, the thermal stability and polymorphic transformation kinetics in β-MnTe films obtained via radiofrequency magnetron sputtering were investigated. The obtained MnTe films with a composition range of 50.5-46.1 at.% Te exhibited a single β phase. The polymorphic transformation temperature from the β (wurtzite-type) to an α (NiAs-type) phase decreased with increasing the Te content. In the non-isothermal analysis using differential scanning calorimetry, the activation energy for β → α transformation was measured to be 1.41 eV, based on Kissinger plots. The retention time of β-MnTe was also investigated via the Ozawa method, and it was estimated to be retained for 4.5 109 years at 25 C. The estimated Avrami exponent of 3.5 indicated that two- and three-dimensional growth at a constant nucleation rate was dominant at the intermediate stage of β → α transformation.