An analysis is made of the boundary conditions for the envelopes in th
e effective mass method, applied to heterojunctions in a GaAs/AlAs sup
erlattice. These conditions make it possible to find the dependence of
the effect of GAMMAX mixing on the parity of the number of monomolecu
lar layers in an AlAs layer. The dispersion of electrons in the two lo
west minibands is found near a transition for a type-I to a type-II su
perlattice.