Optical properties of GaAs bulk layers and (Al,Ga)As/GaAs quantum wells with well sizes of 80, 100, and 200 A˚ have been studied. The structures were grown on (100) oriented Ga doped Ge substrates using molecular beam epitaxy. In contrast to earlier less successful attempts to grow polar semiconductors on nonpolar (100) substrates, the structures prepared in this study had good surface morphologies across the entire substrate and seemed relatively free of nonradiative traps. In bulk and quantum well structures, bound excition and donor‐acceptor transitions were observed. The luminescent intensity at 2 K was comparable to that of similar structures grown on GaAs substrates and dominated by donor‐acceptor (Ge0Ga‐Ge0As) transitions. The ability to successfully grow polar semiconductors on (100) nonpolar semiconductors should provide many opportunities in hybrid and heterojunction device applications.