We report successful fabrication of GaAs/Al0.26Ga0.74As double‐heterostructure laser diodes grown on patterned Si substrates by molecular beam epitaxy. The patterned substrates consist of exposed Si stripes with widths ranging from 9 to 70 &mgr;m and surrounded by 900 A˚ of SiN films on both sides. Oxide‐defined contact stripe lasers with stripe widths ranging from 3 to 50 &mgr;m (corresponding to each of the SiN‐defined stripe windows) were fabricated. Reduction of laser threshold current densities compared to similar lasers grown on nonpatterned Si substrates is observed, and is attributed to current confinement effect by the high‐resistivity polycrystalline GaAs/AlGaAs films surrounding the active devices. From the measurements on the longitudinal mode spectrum and far‐field patterns, lateral index guiding is also observed for the 10‐&mgr;m‐wide selective‐area grown laser.