  The ground-state phase diagram of a half-filled anisotropic Kondo lattice
model is calculated within a mean-field theory. For small transverse exchange
coupling $J_{\perp}<J_{\perp c1}$, the ground state shows an antiferromagnetic
long-range order with finite staggered magnetizations of both localized spins
and conduction electrons. When $J_{\perp}>J_{\perp c2}$, the long-range order
is destroyed and the system is in a disordered Kondo singlet state with a
hybridization gap. Both ground states can describe the low-temperature phases
of Kondo insulating compounds. Between these two distinct phases, there may be
a coexistent regime as a result of the balance between local Kondo screening
and magnetic interactions.
