Ultra-high-Q optical resonators have played an important role over a wide range of research fields including nonlinear optics, cavity optomechanics, quantum information and optical telecommunications. Recently, it has been demonstrated that this essential components can be implemented on a chip in different forms based on semiconductor fabrication technology. We also demonstrated wedge disk resonators of around 900 million Q on a silicon chip and successfully performed initial works with the resonators to develop narrow line width lasers, reference cavities for frequency stabilization, micro-comb, and stable microwave synthesis. In this talk, these previous works and future research directions on ultra-high-Q resonators and their application will be presented and discussed including works on low-loss waveguides on a silicon chip. In addition, the current efforts will be introduced, to extend the operation wavelength of the on-chip ultra-high-Q resonators and low loss waveguides from the near-IR to the mid-IR based on the hybrid material system to apply well-matured micro- fabrication technique to untamed materials of good optical properties in the mid-IR.