Flash sintering is extensively investigated for over a decade since its discovery, but its practical application is seldomly discussed. A primary challenge in utilizing flash sintering is a difficulty in sintering large samples. This is since in a typical direct current (DC) flash sintering, the current is concentrated primarily in the center of the sample, causing a significant temperature gradient between the interior and surface of the sample, thus leading to an inhomogeneous microstructure in the final product and sometimes large stresses in the sample that breaks the material. In this paper, we utilized the alternating current (AC) with varying frequencies to investigate its effect on this inhomogeneity issue in flash sintering. The results indicate that increasing the frequency significantly enhances the uniformity of the sample. The underlying mechanism is related to a significant “skin effect” in AC flash sintering, where the current density is concentrated on the surface of the sample rather than its center, compensating for a higher radiation heat loss at the surface and resulting in a more uniform sample temperature. This work provides a potential approach to enhance the flash sintering for industrial applications.