The deformation behavior of single crystals of WSi2 has been investigated as a function of crystal orientation in the temperature range from room temperature to 1500 degrees C in compression. Single crystals of WSi2 can be deformed only at high temperatures above 1100 degrees C, in contrast to MoSi2 in which plastic flow is possible even at room temperature. Four slip systems, {110}[111], {011}[100], {023}[100] and (001)[100], are identified. While the former three slip systems are operative also in MoSi2, the (001)[100] slip is only operative in WSi2. The (001)[100] slip in WSi2 is the alternative to {013}[331] slip in MoSi2 since they are operative in the same orientation range. Slip on {110}[331] is hardly observed in WSi2. The values of critical resolved shear stress (CRSS) for the commonly observed slip systems are much higher in WSi2 than in MoSi2 with the largest difference for {110}[111] slip. The higher CRSS values in WSi2 are not only due to the intrinsic difference in the deformation behavior but also due to the existence of numerous grown-in stacking faults on (001). (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.