The dynamic behavior of &agr;, &bgr;, and screw dislocations in both undoped and doped InP is investigated. The generation of dislocations from a surface scratch is suppressed in doped InP. This effect is attributed to the immobilization of dislocations due to locking by impurities similar as observed in GaAs. Isovalent Ga and As dopants are found not to affect the dislocation velocity. Zn acceptors strongly reduce the dislocation velocities of all type of dislocations while S donors enhance the velocity of &agr; dislocations and reduce the velocity of &bgr; and screw dislocations. Such impurity effects are in contrast with those observed in GaAs. The measured dislocation velocities are expressed with a simple empirical equation as a function of stress and temperature. The mechanical strength of InP reflects the above dynamic behavior of individual dislocations. An increase in the yield strength results from a decrease in the dislocation velocity in Zn‐doped InP. On the other hand, an increase in the strength at high temperatures results from dislocation immobilization in Zn‐ or S‐doped InP.