The temperature distribution in a melt of PbMoO₄ is investigated using a modified thermocouple and a scanning device. It is shown that the PbMoO₄ melt whose thermal field is significantly inhomogeneous at different depths demonstrates a strong (below the melting temperature) supercooling at the surface due to the evaporation. The position of the isotherm corresponding to the melting temperature of PbMoO₄ in the melt is determined by the degree of the melt supercooling at different growth parameters. The results obtained show that the conditions of mass and heat exchange in the melt are mainly determined by convection. The free convection remains dominant even at intense rotation of a crystal and the most thorough thermal isolation of the crystallization unit.