The thermoelectric power of a Luttinger liquid with a potential barrier is calculated. The long-range nature of electron-electron interaction is taken into account. It is shown that the increased interaction range changes the temperature dependence of the thermoelectric power qualitatively. At low temperatures, the Seebeck coefficient of a Luttinger liquid is considerably smaller than that of a one-dimensional Fermi gas. As the temperature increases, the thermoelectric power increases rapidly and can exceed that of a Fermi gas. The results obtained are in qualitative agreement with experimental data for quasi-one-dimensional 5-nm-thick InSb wires.