A bottom‐up strategy for the preparation of hierarchical hybrid materials with good thermostability is reported. The hybrid molecule was constructed from a Wells–Dawson‐type polyoxometalate (POM) cluster and a poly(ethylene glycol) (PEG) chain through covalent‐bond formation. The large distinction between the POM cluster and PEG chain results in a microphase separation to form POM and PEG layers that further alternatively arrange into hybrid lamellae with a sub‐20 nm thickness. Then the hybrid lamellae could simultaneously organize into spherulitic superstructures. Because of this hierarchical structuring, strong electrostatic interactions between POM clusters are maximized within the POM layers. This gives rise to thermostability. Structurally, the hybrid lamellae and the superstructures are unchanged, even at 160 °C, and indeed the shear storage modulus of the hybrid material remains nearly constant within this same temperature range. This study demonstrates the concept of bottom‐up hybridization, in which rationally selecting building blocks, designing the hybrid molecule, and then manipulating hierarchical structures can generate thermostable hybrid materials.