We demonstrate the first room‐temperature low‐threshold continuous‐wave (cw) operation of Al0.3Ga0.7As/GaAs single quantum well (SQW) heterostructure lasers grown by metalorganic chemical vapor deposition (MOCVD) on Si substrates using techniques of SiO2back coating and thermal cycle annealing. The all‐MOCVD‐grown SQW lasers on GaAs/Si with etch pit density of 1.5× 107cm−2have threshold current as low as 55 mA (1.41 kA/cm2) under cw at room temperature. The SiO2back coating is effective to obtain excellent current‐voltage characteristics. Thermal cycle annealing is also found to improve the crystallinity of GaAs/Si and to contribute to room‐temperature cw operation of the lasers on Si substrates.