Abstract: The Si/SiGe quantum cascade laser is a new coherent IR source based on intersubband transitions, which overcomes the limitations imposed by the indirect gap. This laser will have a great impact on the development of terahertz devices and indicates a possible way to integrate active terahertz devices into silicon-based technology. In this paper we will describe the principle and latest progress in the active layer design, materials growth, and waveguide fabrication of this Si-based laser.