An analytic semiempirical expression is developed for the ground-state potential-energy surface of the Ks system. Use is made of the valence-bond formulation with the inclusion of overlap and three-center terms. The diatomic Coulomb and exchange integrals are estimated from accurate values for the Hj molecule by a modified London-Eyring-Sato procedure, while the three-center integrals are approximated by simple formulas. A linear, symmetric saddle-point configuration of minimum energy is found that has properties in approximate agreement, though not identical, with other estimates from theory and experimental rate data. The details of the surface are presented in terms of contour maps for a variety of distances and angles. Because of the inclusion of overlap and three-center terms, a more realistic energy is expected for the nonlinear configurations than could be obtained from previous potential energy formulas. The utility of the present method for dynamical studies of reaction cross sections is indicated.