The paper gives a brief analysis of current concepts on the process of melt ordering and structural self-organization at the temperature close to melting point, including that within the interface area when growing semiconductor single crystals. The experimental data presented confirm the existence of ordered multi-atomic growth units (clusters) in the melt under the conditions close to undisturbed equilibrium crystallization. The conclusion is justified on the prospects of studying the clustering processes within a melt in microgravity. A mathematical model of convective mass transfer is proposed as an independent investigation tool. This model includes the equations of hydrodynamics, impurity transfer and convective flow within the interface transient area. Materials properties and the temperature are presented as a single-value function of enthalpy. For the first time the melt structural model near the crystallization front considers the availability of clusters formation (CF) that cause resistance to the melt flow. This resistance of medium is described by means of specific double-phase coefficient introduction depending on the enthalpy value in each assigned mesh micro-volume under calculation. Basing onto our previous space growth experiments aboard the Photon series satellites (J. Crystal Growth 205 (1999) 497; 223 (2001) 29), the necessary empirical model parameters are evaluated. The results of CF-model testing are demonstrated, including the description of real orbital and ground-based GaSb:In crystallization experiments. (C) 2004 Elsevier B.V. All rights reserved.