Commercially available silicon carbide (SiC) crystals are produced by the physical vapor transport (PVT) or seeded sublimation process. Especially, bonding the seed substrate to the graphite seed holder is one of the most important processes to suppress generation of defects and dislocations in the PVT growth. The pores in the seed/graphite holder interface often form via degassing from carbon glue during baking process. The pores act as a thermal resistance which forms macro-defects in the grown crystal.[1] Since the wafer diameter on the market is changing from 6- to 8-inch, severe control of the seed bonding process is required. It is important to understand how the pores affect the thermal field of a growing crystal. In this study, we investigated an effect of interfacial pores on thermal field and crystal-shape uniformity in the initial growth stage by the Virtual Reactor (VR) simulation software.[2] Figure.1 shows a schematic illustration of (a) a crucible model used for PVT growth and (b) the model of the interfacial-planer-shaped pore (IP) filled with argon. Model parameters on the simulation were listed in table.1. The macro-defect formation from the pores was not considered in this simulation. The ratio of the thickness just above the IP (dIPC) to the growth thickness at the center of the crystal (dSC) was used to crystal-shape uniformity and named” the uniformity index” here. Figure 2 shows the simulated crystal shape on the 1.5 mm-thick seed after PVT growth of 30 hours. Without the IP, grown crystal shape was smooth convex. On the other hand, grown crystal shape was locally concave just above the IP. The difference in thermal resistance arises by the IP resulted in a decrease in growth rate and a clear difference in crystal shape. It is confirmed that the IP greatly affects to thermal field around seed, as a result, the crystal surface would be distorted for this condition. We investigated the uniformity index with different seed thickness. Figure 3 shows the relationship between the seed thickness and the dIPC/dSC ratio for growth time of 30 hours. For thinner seed thickness, the dIPC/dSC ratio becomes clearly lower. As increasing seed thickness, the dIPC/dSC ratio also increases and is getting closer to the unity, which means crystal-shape uniformity is improved. This result suggests that thicker seed can improve the uniformity of grown crystals, even if interfacial pores exist. These results provide a guideline for the control of interfacial pores in the actual crystal growth.