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Metal halide perovskites (MHPs) are plausible candidates for practical p‐type semiconductors. However, in thin film transistor (TFT) applications, both 2D PEA2SnI4 and 3D FASnI3 MHPs have different drawbacks. In 2D MHP, the TFT mobility is seriously reduced by grain‐boundary issues, whereas 3D MHP has an uncontrollably high hole density, which results in quite a large threshold voltage (Vth). To overcome these problems, a new concept based on a 2D–3D core–shell structure is herein proposed. In the proposed structure, a 3D MHP core is fully isolated by a 2D MHP, providing two desirable effects as follows. (i) Vth can be independently controlled by the 2D component, and (ii) the grain‐boundary resistance is significantly improved by the 2D/3D interface. Moreover, SnF2 additives are used, and they facilitate the formation of the 2D/3D core–shell structure. Consequently, a high‐performance p‐type Sn‐based MHP TFT with a field‐effect mobility of ≈25 cm2 V−1 s−1 is obtained. The voltage gain of a complementary metal oxide semiconductor (CMOS) inverter comprising an n‐channel InGaZnOx TFT and a p‐channel Sn‐MHP TFT is ≈200 V/V at VDD = 20 V. Overall, the proposed 2D/3D core–shell structure is expected to provide a new route for obtaining high‐performance MHP TFTs. [ABSTRACT FROM AUTHOR]