  The ground-state electronic configuration of three coupled bidimensional
electron gases has been determined using a variational Hartree-Fock approach,
at zero magnetic field. The layers are Coulomb coupled, and tunneling is
present between neighboring layers. In the limit of small separation between
layers, the tunneling becomes the dominant energy contribution, while for large
distance between layers the physics is driven by the Hartree electrostatic
energy. Transition from tunneling to hartree dominated physics is shifted
towards larger layer separation values as the total bidimensional density of
the trilayers decreases. The inter-layer exchange helps in stabilize a
"balanced" configuration, where the three layers are approximately equally
occupied; most of the experiments are performed in the vicinity of this
balanced configuration. Several ground-state configurations are consequence of
a delicate interplay between tunneling and inter-subband exchange.
