With the help of Thermo-Calc software and based on the thermodynamic database of the Al-Ga-In-P-As-Sb-C-H system, the compositional spaces under conditions of different temperatures and pressures can be calculated and analyzed in the cases of stable, metastable equilibria, or irreversible reactions. Compared with traditional methods, more information can be obtained from the present calculation. Such information is useful to computer-assisted design for metalorganic vapor phase epitaxy (MOVPE) processing of III-V semiconductors.