The ground state energy of a shallow donor pair in semiconductor with
anisotropic effective mass is calculated in the framework of the effec
tive mass theory. The energy is found to be minimal if the axis of the
pair is orthogonal to the direction corresponding to the greatest val
ue of the effective mass. It is concluded that the electronic structur
e of donor molecule in a many-valley semiconductor depends on the mole
cule orientation with respect to the crystallgraphic directions.