During the past year, the work on the use of Gas Source Molecular Beam Epitaxy (GSMBE) for the growth of GaInAs(P)/InP heterostructures has extended to the detailed study of a variety of heterostructures. This paper reviews some of the results of these studies. There has been a demonstration of single quantum wells as thin as 5 Å for both Ga 0.47In 0.53As and Ga x In 1 − x As y P 1 − y with near monolayer abruptness. Superlattices of these materials have been reported for the first time with the observation of exciton structure in the absorption and photoresponse spectra. Studies of carrier transport normal to the plane of the superlattice show the behavior of carriers at individual well sites for the first time. Superlattice avalanche photodiodes with high gain and low dark current have been demonstrated, as have heterostructure bipolar transistors with dc properties superior to any previously reported, and potential for superior high frequency performance. Also described, are some of the results of recent studies of two types of gas sources for generating group V dimer beams by the decomposition of AsH 3 and PH 3.