Si doped GaAs single crystal with diameter over 200 mm was prepared by vertical gradient freeze (VGF) method. The 8 inch GaAs single crystal substrate was obtained through multi-line cutting, edging, grinding, chemical mechanical polishing and wet cleaning. The crystal quality, dislocation density, electrical properties and surface quality of 8 inch GaAs substrate were characterized by X-ray diffraction, dislocation density inspection, Hall measurement, non-contact surface resistivity measurement, photoluminescence and wafer surface defect inspection. The results show that the full width of half maximum (FWHM) of substrate (400) diffraction peak is smaller than 0.009°, the average dislocation density is lower than 30 cm-2, the lowest dislocation density is 1.7 cm-2 and 98.87% area are zero dislocation. Moreover, the standard deviation of surface resistivity and photoluminescence intensity are smaller than 6% and 4%, respectively. The number of the spot with light point defect (LPD)≥0.2 μm is less than 10. The results show that the 8 inch semiconducting GaAs single crystal substrate with excellent performance is developed and can be used as the high quality substrate for epitaxial growth and devices fabrication.