This paper reports a direct determination of the relative, static permittivity of the atomic lattice of InSb at 77°K. The measurements were performed on relatively pure (ND≤1014cm−3)n‐type single‐crystal samples at 70.1 GHz by utilizing a strong magnetic field (∼40 kG) to immobilize the charge carriers in a direction parallel to the applied TE01°‐mode electric field. In this manner, the rf losses normally associated with ``drift'' motion of the charge carriers were made negligible, thus permitting the lattice component of the permittivity to be accurately resolved. The measured relative value, &egr;s=17.78±0.15, compares favorably with several values previously calculated from measurements of the ir reststrahlen spectrum.