The quest for new transition metal dichalcogenides (TMDs) with outstanding electronic properties is a particularly significant and interesting subject. The use of nonconventional methods of materials synthesis, especially pressure engineering, shows great potential for breakthrough discoveries in TMDs. Here, we employ the high-pressure techniques to successfully realize the transformation of two-dimensional semiconductor into three-dimensional superconducting states in $1T\text{−}{\mathrm{HfSe}}_2$. We unambiguously demonstrate that the enhancement of the interlayer coupling and the bonding between interlayer Se-Se atoms contribute to the emergence of nonlayered $C2/m$ and $I4/mmm$ phases. The discovered three-dimensional (3D) structures present excellent superconductivity compared to the original layered structure, and the superconducting critical temperature reaches a maximum of 5.8 K at around 50 GPa. Theoretical calculations reveal that the realization of superconductivity in these two 3D structures is related to the increase in the density of states at the Fermi surface $\left[N\left({\varepsilon }_f\right)\right]$. The present results in ${\mathrm{HfSe}}_2$ may provide a platform for our deep understanding of the relationship among dimensionality, structure, and superconductivity phenomena in TMDs.

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• Order parameters
• Phase diagrams
• 2-dimensional systems
• Transition metal dichalcogenides