The experimental data, obtained by the method of adiabatic drop-calorimetry over the temperature range of 670-1100 K, including the solid and liquid states, are analyzed to reveal a structure of subeutectic alloy of Al-Si system (8.9 molar % Si). Variations of enthalpy are measured relative to the base temperature of 293.15 K with the isothermal holdings in each measurement of 10 min. The experimental data are compared with the computed ones for different model states of melt (mixtures of solid and liquid phases of eutectic, monodispersed emulsion and homogeneous solution). The best compliance is obtained for the inhomogeneous two-phase structure.