Wetting phenomena and the effect of alumina surface orientation on the wettability in Si/alpha-Al2O3 system were studied by an improved sessile drop method using R(0112), A(1120), C(0001) faces of single crystals and polycrystals at 1723 K in a reducing Ar-3% H-2 atmosphere. The contact angles show a vibration behavior for all the single crystals but to a less extent for the polycrystals. The extent of the vibration correlates not only with the reaction intensity but also with the stability of the Si droplet on the alumina surfaces. The interfacial reaction leads to the formation of a series of reaction rings, which is more serious at the single crystal surfaces. More importantly, the wettability is dependent on the alumina surface orientation, with the intrinsic contact angles being about 98 +/- 2 degrees, 101 +/- 1 degrees, 69 +/- 1 degrees, and 98 +/- 2 degrees, respectively, for the R(0112), A(1120), C(0001) and polycrystal alpha-Al2O3 substrates. The much smaller contact angle for molten Si on the C(0001) surface is explained by the favorable reduction in the Si/alpha-Al2O3 interfacial free energy by the terminated and enriched aluminum atoms at the reconstructed C-(root 31 x root 31) R +/- 9 degrees surface. The importance of the aluminum presence at the Si/alpha-Al2O3 interface to the wettability of this system was further demonstrated by a substantial improvement in the wettability of the R(0112)alpha-Al2O3 substrates by Si-Al alloys.