Indium selenide (${\mathrm{In}}_2{\mathrm{Se}}_3$) exhibits significant phase transition behavior and relatively weak interlayer interactions, resulting in greater compressibility under pressure compared to other transition metal dichalcogenides. Hydrostatic pressures up to 11.9 GPa were applied to probe the structural evolution and stability of $\alpha /\beta \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ van der Waals heterojunctions. The shift of the $A_1^3$ mode to the $E_g^2$ mode near 2 GPa marks the transformation of $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ into ${\beta }^{\prime }\text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$. The disappearance of the $E^2, A_1^2$, and $E^4$ modes around 6 GPa signals the subsequent transition to $\beta \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$. The Raman intensity mapping of the $A_1^1 \to A_g^4 \to E_g^2$ mode under pressure further delineates the complete phase transition pathway, confirming that the heterojunction remains stable between 0 and 2 GPa and converts entirely to $\beta \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ beyond 6 GPa. Finally, an intrinsic correlation mechanism among pressure, structural distortion, electronic band structure, and thermodynamic stability is established via first-principles calculations. These findings advance the understanding of stress-mediated structural evolution in $\alpha /\beta \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ heterojunctions and support the design of strain-engineered devices.

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• High-pressure studies
• Phase transitions
• van der Waals systems
• Spectroscopy