Group 13 trihalides MY 3 (M = Al, Ga, and In; Y = Cl, Br, and I) mostly having a dimeric M 2 Y 6 molecular structure in the solid state and a mixture of M 2 Y 6 dimers and MY 3 monomers in the vapor phase are potential candidates for entropy-driven liquid−liquid transition M 2 Y 6 ⇄ 2MY 3 at elevated temperatures. Using pulsed neutron diffraction and high-energy X-ray scattering supported by structural modeling, we show a dimer molecular structure of liquid GaCl 3 above the melting point at 351 K and midway between the boiling point (474 K) and the critical temperature (694 K) with almost hidden characteristic evolution toward a possible liquid−liquid transition. In contrast to edge-sharing (ES) dimers in solid and vapor of D 2h symmetry, the ES Ga 2 Cl 6 molecules in the melt have a puckered structure of the central four-membered ring with shorter Cl−Cl (2.90−3.09 Å) and longer Ga−Ga (3.20−3.26 Å) second-neighbor correlations. The elongation of Ga−Ga intramolecular distances with increasing temperature simultaneously with diminished Cl−Cl nearest neighbor contacts destabilizes the ES dimers, indicating the first step toward dimer dissociation.