The effects of speed of growth of silicon sheet crystals on crystal quality are discussed. It is pointed out that thermal stress and its effects increase, and that the stability of the interface decreases with increasing rate of advance of the interface. These two principles are discussed in relation to two growth configurations: that in which the solid-liquid interface is perpendicular to the plane of the sheet, and that in which it is inclined. It is concluded that increased speed within the range that is relevant to sheet growth causes degradation in crystal quality.