Lately, the thermoelectric community has been fascinated by the Germanium-tellurides (GeTe-based alloys) which feature high electrical conductivity and high thermal conductivity. Additionally, the GeTe undergoes a phase transition from the low-temperature rhombohedral α-GeTe to high-temperature cubic β-GeTe at 673 K, which induces the discontinuities in temperature-dependent TE property curves. In this work, the GeTe is doped with multiple dopants (e.g., Sb, Cu, Se, Bi, Ga, Mn, Sn.) via long-term heat treatment, and we further realized that the α-to-β phase transition could be greatly affected by the dopants. For example, the addition of Sb, Se, and Mn effectively lower the α-to-β phase transition temperature, and can be viewed as stabilizers for cubic β-GeTe. The compositional homogeneity and microstructural texture for α-GeTe and β-GeTe varies dramatically in those Sb-, Se- and Mn-doped GeTe, which eventually leading to a wide distribution in their zT peak values, ranging from 0.8 to above 2.