Two compounds with the sphalerite structure, ZnSe (ao = 5.667 Å, ionicity factor fi = 0.676) and Zn-Te (ao = 6.101 Å, fi = 0.546) have been plastically deformed and the induced dislocation substructure has been studied by TEM. The samples with low dislocation density have been pre-deformed at 588 K for ZnSe and at 430 K for ZnTe and then deformed at lower temperature, 293 K for the two compounds. The activation parameters show that in the temperature range, Peierls friction stresses control the deformation. For the two compounds, the photoplastic effect is evidenced. Using weak-beam electron microscopy the glide dislocations are studied. From the measured dissociation width the stacking fault energy is calculated. As for the III-V compounds the low value of the reduced stacking fault energy can be related to the bond ionicity