The status of monolithic GaAs/Si (MGS) integration is reviewed and its future prospects are discussed. The MGS material now available is satisfactory for majority-carrier devices, but improvement in quality is needed for minority-carrier devices. By using a suitable sequence of processing steps, fabrication of GaAs MESFETs and Si MOSFETs on the same wafer and monolithic integration of GaAs/AlGaAs double-heterostructure LEDs and Si MOSFETs have been achieved. The GaAs and Si FETs show characteristics comparable to those for devices fabricated on separate GaAs and Si substrates. The LEDs have been modulated up to 27 Mb/s by applying a pattern of voltage pulses to the MOSFET gate. Two promising applications of MGS integration are optical interconnects between Si VLSI chips and monolithic microwave integrated circuits. Much better performance should be obtained by operating MGS ICs at liquid nitrogen temperature.