Anisotropy effects on the reliability of single-crystal silicon were investigated by means of scratch tests along [110] and [100] crystallographic directions. It was found that fracture (partial cone cracks) starts along favoured {110} and {111} cleavage planes, with crack orientation varying upon the scratching direction. Moreover, the [100] direction was found to be twice as reliable as the [110] direction. Stress and phase analyses were carried out to explain this effect, which has implications for the design of silicon-based devices.