is a ceramic material that is used extensively in industrial applications, due to its excellent optical, electrical, and thermal properties. 1 Particularly, transparent Y 2 O 3 ceramics exhibit outstanding optical transmission over a wide range of wavelengths, with an excellent signal-to-noise ratio. 2 In addition, as a host material of high-powder laser gain media, research into transparent polycrystalline Y 2 O 3 is being actively conducted. [3][4][5] Facilitating laser oscillation for transparent ceramic requires light transmittance equivalent to that of a single crystal, which is close to the theoretical value. Laser oscillation is difficult because oscillation hardly occurs even if only 0.1% of pores remain in transparent functional ceramics. It is difficult to make transparent ceramics that are manufactured only by sintering using powder as a raw material due to the difficulty of completely removing pores. Thus, various sintering techniques have been developed to fabricate high-quality transparent polycrystalline ceramics. Among them, spark plasma sintering (SPS), which is also called field-assisted sintering technology (FAST) or pulsed electric current sintering (PECS), can be applied to efficiently fabricate highly densified pellets using advanced sinterability. In the SPS process, due to the applications of mechanical pressure and electrical current, full densification can be achieved at lower temperatures with finer microstructures, as compared to the conventional sintering process. [6][7][8] However, some serious problems have also been reported including nonuniform sintering. 9-11 When Al 2 O 3 and Y 2 O 3 were sintered at high heating rates, nonuniform appearance and microstructure of the translucent periphery and opaque center were observed. The opaque central region contains many large pores, which lower the optical transmission significantly. In order to fabricate transparent ceramics for optical applications, such pores should be removed, and uniform sintering should be achieved.Considerable research to improve the uniformity and optical properties of sintered bodies by optimizing the detailed conditions of the SPS process has been reported. [12][13][14][15][16] There is also a fundamental solution to the problem of decreasing the heating rate or changing the holding times; however, research has reported the application of the two-step sintering