Semiconductor microcavities can restrict photons in a small volume compared to the wavelength of light, and can artificially adjust the spontaneous emission characteristics of the active medium in the cavity, which is important for the development of more efficient optoelectronic devices. At the same time, semiconductor microcavities also provide a good platform for the fundamental research of cavity quantum electrodynamics. Optoelectronic devices based on semiconductor microcavity have been widely used, such as microcavity lasers, microcavity sensors, microcavity optical filters, etc. Optical microcavities are usually divided into three types: Fabry-Pérot (FP) microcavities, Photonic Crystal (PC) microcavities, and Whispering-gallery Mode (WGM) microcavities. In WGM semiconductor microcavities, photons circulate along the sidewall of the waveguide layer, and the optical field is confined by total reflection at the interface between the waveguide layer and the surrounding air. Therefore, WGM microcavities can achieve high quality (Q) value and small mode volume. Compared with the FP and PC microcavities, WGM microcavities have the advantages of simple structure, convenient preparation, and easy integration with large scale optoelectronic circuits. GaN based semiconductor materials are featured with direct wide bandgap, including aluminum nitride, gallium nitride, indium nitride, and a variety of alloys between them. By adjusting the composition of the alloy, the emission wavelength can cover from deep ultraviolet to the near-infrared band. They are very important for the preparation of optoelectronic devices. In addition, GaN based semiconductor materials with high exciton binding energy and oscillator strength can be combined with WGM microcavity to achieve micro-cavity optoelectronic devices with small size and high efficient, which can be used for cavity quantum electrodynamics studies at room temperature. Therefore, GaN-based WGM microcavity light-emitting devices have attracted the attention of many researchers, and have been widely used in optoelectronic integration, spectral analysis, and other fields.To date, there have been many reports about GaN microdisk based lasers and sensors on Si, and laser emission wavelengths have covered from UVC to the green spectral range. However, GaN based microdisk cavities on Si are also faced with many difficulties, including the lattice constant mismatch and thermal expansion coefficient mismatch between GaN and Si substrates, and the melt etching during epitaxial growth, etc. There is a 17% lattice mismatch between GaN and silicon, usually resulting in a high threading dislocation density (typically 1 010 cm^-2) during epitaxial growth. This can reduce the internal quantum efficiency of the active region, and cause the interface roughness of the GaN film, thus increasing the scattering loss of the microcavity. On the other hand, the thermal expansion coefficient mismatch between GaN and Si substrate is as large as 54%, which leads to large tensile stress in GaN film during the cooling process after epitaxial growth, resulting in wafer warping and even cracking. Therefore, to ensure the quality of the active region, it is usually necessary to grow thick stress adjustment and defect filtration layers. Moreover, the Ga source used in epitaxial growth can corrode Si substrate, that is, melt etching. A certain thickness of AlN buffer layer is usually grown to protect Si substrate before GaN growth. As a result, the total thickness of GaN epitaxial layer on Si substrate is large (generally >1 μm). The large thickness of microdisk makes it difficult to guarantee the single-mode operation, and can reduce the light confinement ability and microcavity effect. In addition, the nitrides near the substrate often have high density defects and dislocations, and their internal optical absorption and scattering losses can be large. This can also affect the Q factor and the threshold of the microdisk laser.To solve the above problems, a new method of device preparation is proposed in this study. Devices fabricated by this method avoid the influence of poor crystal quality and large thickness of GaN layers directly grown on Si substrate. Sapphire substrate is used for the GaN growth in this study to ensure crystal quality. During the fabrication of microdisks, the epitaxial layer was transferred to the Si substrate, and the rich defect layer close to the substrate during the original growth was removed. After that, a simple SiO₂ sacrificial layer wet etching technique was used to realize the air gap structure between GaN microdisk and Si. High Q GaN microdisk cavity on Si with low lasing threshold was successfully realized under the condition of optical pumping. The cavity Q factor is up to 10 487. The device threshold energy is as low as 5.2 nJ/pulse, corresponding to an energy density of 33.6 μJ/cm². Owing to the good crystal quality and low cavity losses, the device can still maintain excellent laser characteristics at 100 ℃. The device preparation method in this study also has good flexibility, and the GaN-based microdisk resonator can be fabricated on different kinds of substrates, such as metal, polymer, quartz, etc.