In order to obtain the SI-GaAs material with high resistivity and mobility, the VGF(Vertical Gradient Freeze) method was used to grow the SI-GaAs single crystal which the polycrystalline for growth were come from the high pressure synthesis method and the HB synthesis method. Then the concentration of EL2, carbon and resistivity, mobility of the corresponding single crystal chips were tested and analyzed, and the influence of the different GaAs stoichiometric on concentration of EL2 and electrical parameters of the single crystal was compared and analyzed. After several times of experiments, the concentration reasonable scope of EL2 and carbon under the condition of the resistivity greater than >1×108 Ω?cm and the mobility greater than 5×103 cm2/(V?s) were determined. Finally, the experiment conclusion was used to guide the single crystal growth of SI-GaAs which used for MBE epitaxial growth, and what’s more, realizing the crystal growth having a great repeatability and consistency on high resistivity and mobility.