A metal organic chemical vapor deposition apparatus comprising a source ampule, a liquid micro-pump, a vaporizer equipped with a solvent supply means, and a reactor. A reactant dissolved in a solvent in the source ampule is transferred to the vaporizer by the liquid micro-pump. A sufficient amount of the solvent is additionally fed to the vaporizer by the solvent supply means, concurrently with the transfer, and vaporized along with the reactants. After being vaporized in the vaporizer, the reactant is injected to the reactor by carrier gas and deposited on a semiconductor substrate to form a high dielectric thin film. By virtue of the additional supplied solvent, the recondensation of the reactant in the vaporizer, which is attributed to the separation of the solvent from the reactant, can be prevented in the vaporizer and in the transfer line between the vaporizer and the reactor. In addition, the residues of the reactant, which may result from the separation, can be washed off by providing the solvent through the supply means to the vaporizer.