The Vickers microhardness was measured on the basal (0001) plane of sapphire single crystals in the temperature range from 25$^{circ}C$to 1000$^{circ}C$. The substructure surrounding the indents was investigated using selective chemical polishing and etching, optical microscopy, and trasmission electron microscopy (TEM). At room temperature, cracks were predominant, and at intermediate temperatures (400$^{circ}C$and 600$^{circ}C$), extensive rhombohedral twinning was observed. On the other hand, at higher temperatures, prism plane slip bands on prism plane {1120}(원문참조) were dominant in the microstructure. TEM observations revealed that the dislocation substructure at the vicinity of the indents consisted of fairly straight dislocations lying in basal and/or prism planes and aligned along the <1100> and <1120> directions. The details of the glide dissociation of perfect <110> screw dislocations into three collinear 1/3<1100> partials on the prism plane and the Peierls potential for sapphire single crystals were discussed.