  The Fermi surface of rare-earth tri-tellurides ({\it R}Te$_{3}$) is
investigated in terms of the nesting driven charge-density wave formation using
positron annihilation and first-principles LMTO calculations. Fermi surface
nesting is revealed as a strong candidate for driving charge-density wave
formation in these compounds. The nesting vector obtained from positron
annihilation experiments on GdTe$_{3}$ is determined to be ${\mathbf q} =
(0.28\pm0.02,0,0) {\mathbf a}^{*}$, (${\mathbf a}^{*}=2\pi/{\mathbf a}$), in
excellent agreement with previous experimental and theoretical studies.
