The mean-square optical anisotropy (Gamma (2)) was determined from anisotropic light scattering measurements for nine samples of poly(n-hexyl isocyanate) (PHIC), a typical semiflexible polymer, in the range of weight-average molecular weight from 1.65 x 10(4) to 1.04 x 10(5) in n-hexane at 25.0 degreesC. It was found that the behavior of the ratio (Gamma (2))/x(w) as a function of the weight-average degree of polymerization x(w) may be satisfactorily explained by the corresponding theory on the basis of the Kratky-Porod wormlike chain model with the respective values 840 Angstrom and 71.5 Angstrom (-1) of the basic model parameters, i.e., the static stiffness parameter lambda (-1) and the shift factor ML, and also with the assigned value 1.1(2) Angstrom (2) of the difference Delta alpha between the polarizabilities, per unit contour length, parallel and perpendicular to the chain contour. The above value of Delta alpha is appreciably larger than its value 0.5(3) Angstrom (2) estimated from the bond polarizabilities on the basis of the chemical structure of PHIC, indicating that there exists definitely some additional scattered intensity arising from the effect of collision-induced polarizabilities. However, this does not affect the dependence itself of (Gamma (2))/x(w) on x(w). From a comparison of the present results for PHIC with previous ones for typical flexible polymers, it is seen that the difference in the behavior of (Gamma (2))/x(w) between them arises from that in chain stiffness.