In this report, we present a monolithic integration method for a Si-MOSFET and a GaN-LED onto a Si/SiO 2/GaN-LED wafer as an elemental technology for monolithic optoelectronic integrated circuits. To enable a Si-MOSFET device process, we investigated the thermal tolerance of a thin top-Si and GaN-LED layer on a Si/SiO 2/GaN-LED wafer. The high thermal tolerance of the Si/SiO 2/GaN-LED structure allowed for the monolithic integration of a Si n-MOSFET and a GaN-µLED without degrading the performance of either device. A GaN-µLED driver circuit was fabricated using a Si n-MOSFET and a µLED of 30× 30 µm 2, with the modulation bandwidth of the circuit estimated to be over 10 MHz.