The energy bands of the zinc blende structure are treated by the simplified LCAO method of Slater and Koster. A model of the chemical bond is proposed for the purpose that the matrix elements involved may be expressed in terms of certain parameters of the chemical bonds. The energy levels of a number of points in the Brillouin zone are investigated. With this approach, we discuss the variation of the band gap as well as the position shift of the conduction band edge with the change of chemical compositions.