The distortion in bondlength is calculated for a wide range of impurities, both isovalent and heterovalent, in all I-VII, II-VI and HI-V compound semiconductors and in elemental semiconductors, silicon and germanium. Universal parameter tight binding (UPTB) theory of Harrison combined with the spring constant model is used. The results agree well with earlier theoretical estimates and also with the available extended X-ray absorption fine structure (EXAFS) data. A systematic behaviour of the bondlength distortion of impurities in semiconductors with respect to (i) the difference in covalent energy of the host-impurity bond, (ii) the difference in electronegativity between the host and that of the impurity atom and (iii) the change in covalency of the bond when the impurity replaces the host is observed.