Low threshold, optically pumped laser oscillation has been obtained using AlGaAs/GaAs double heterostructures grown on Ge‐coated Si substrates. The optical pump power for threshold is comparable to similar heterostructures grown on GaAs substrates. Between 20 and 85 °C the threshold temperature dependence is exponential withT0=160 °C. The laser wavelength and the peak of the spontaneous emission of lasers grown on Si substrates are shifted to longer wavelengths relative to bulk GaAs. This results largely from the strain in the plane of the epilayer produced by the difference in the thermal contraction of the layers and the Si substrate on cooling from the growth temperature.