GaAs/InGaAs quantum-well lasers have been demonstrated by metallorganic chemical vapor deposition on virtual Ge substrates on Si via aspect-ratio trapping (ART) and epitaxial lateral overgrowth (ELO). Laser-structure growth is achieved in two steps: The first step is growing uncoalesced defect-free Ge stripes on a SiO2 trench-patterned silicon substrate via ART, whereby the misfit defects originating from the Ge/Si interface are trapped by laterally confining sidewalls. Defects arising from above the SiO2 film are reduced by using an optimized ELO process followed by chemical mechanical polishing to provide a planar Ge surface. The second step is overgrowing a GaAs/InGaAs laser structure on the virtual Ge substrate. A number of GaAs/Ge integration issues, including Ge autodoping and antiphase domain defects in GaAs, have been overcome. Despite unoptimized laser structures with high series resistance and large threshold current densities, pulsed room-temperature lasing at a wavelength of 980 nm has been demonstrated using a combination of ART and ELO. This technique is very promising for the achievement of reliable GaAs-based optoelectronic devices on Si. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3129463] All rights reserved.