Cross-sectional scanning tunneling microscopy has been used to investigate the effects of several key growth parameters on the resulting interfacial quality of AlAs/GaAs short period superlattices. For growth on top of AlGaAs layers, only superlattices grown with periodicity no smaller than 4 unit cells of GaAs and 2 unit cells of AlAs and grown with a minimum of 30 s of growth interrupt time are resolved. On the other hand, when grown on top of GaAs layers, superlattices as fine as 2 unit cells of GaAs and 1 unit cell of AlAs grown with only 5 s of-growth interrupt time are resolved. This result suggests that the material on which the superlattice is grown is at least as important as the growth interrupt time. Tn particular, GaAs seems to provide a smoother starting surface than AlGaAs and hence aids in the formation of abrupt interfaces. We also compare our scanning tunneling microscopy data with some predictions based on simple atomic models of the interfacial regions.