The GaAs1 - yPy-InxGa1 - xAS superlattice (SL) system with y = 2x has an average lattice constant equal to that of GaAs, thus allowing the fabrication of lattice-matched strained-layer double heterostructures. This new system can provide a large conduction band-edge discontinuity and higher electron mobility than the AlGaAs-GaAs system. The strained layers and subsequent GaAs layers epitaxially grown on them were found to be of high quality. Light-emitting diodes (LED's), based on this new superlattice, have been fabricated with emission in the wavelength range 0.9-1.1 µm. These LED's have operated for 200 h without any degradation in the output emission intensity. Also a dual-wavelength three-terminal device LED emitting near 0.87 and 0.9 µm has been fabricated. This is one of the first demonstrations of the potential applications of strained-layer superlattices (SLS).