The third order nonlinear susceptibility &khgr;(3)caused by band nonparabolicity is investigated for gallium arsenide‐gallium aluminum arsenide superlattices. Optimization of well width, superlattice periodicity, and barrier height give rise to large nonparabolicities which produce nonlinear susceptibilities comparable to those found in indium antimonide and at least two orders of magnitude larger than bulk gallium arsenide.