Under compression, elemental scandium (Sc) exhibits a remarkable monotonic increase in superconducting critical temperature ($T_c$), at a pressure of 240 GPa, reaching up to 37.6 K—the highest $T_c$ reported for all elemental solids to date. However, its electronic origin underlying this enhancement has remained elusive. Here, by combining first-principles calculations with an analysis of existing superconducting data, we elucidate the electronic mechanism driving pressure-enhanced superconductivity in the crystal structure Sc-III, Sc-IV, and Sc-V. Our in-depth analysis reveals that the increase in $T_c$ is intrinsically governed by progressive $d$-band broadening. Contrary to the conventional view of localized $d$ electrons, extreme pressure induces a substantial interatomic $3d\text{−}3d$ orbital overlap. By evaluating the Kohn-Sham potential barrier, we demonstrate that compression drives the $3d$ electrons to exhibit electronic behaviors analogous to those of $s$ and $p$ electrons toward a nearly free-electron regime, which naturally explains the strong electron-phonon coupling responsible for the rising $T_c$. Our work establishes a direct electronic descriptor for superconductivity in compressed Sc and provides a general framework for understanding pressure-induced phenomena in $d$-block metals.

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• Density of states
• Electronic structure
• Superconductivity
• Superconductors
• First-principles calculations
• Methods in superconductivity