The multiplication and inhomogeneous nuckation of dislocations in silicon crystals have been studied under the actions of mechanical and thermal stresses by the chemical etching method. The experimental results indicate that for the production of multiplication and inhomogeneous nucleation of dislocations, thermal stress is equivalent to mechanical stress. Small-angle grain boundary dislocations, as well as individual as-grown dislocations, can act as dislocation sources. The stress concentration at the defects in the interior of the crystal and at the etch pits on the surface of the crystal can induce dislocation nucleation. Multiplication of screw dislocations may occur in the form of cross-glide. Studies of the spacial geometry of the newly-produced dislocation loops show that the Frank-Read mechanism is probably the primary form for dislocation multiplication.Whether a dislocation multiplies or not depends on the value of the resolved stress component acting on the dislocation source, the temperature and the structure characteristics of the dislocation itself, etc.