Abstract: The first phonon-pumped semiconductor laser. The active region is an unbiased boron-doped Si0.94Ge0.06/Si superlattice with Si0.97Ge0.03 buffer layers embedded in a surface-plasmon strip waveguide. Warm and cool heat sinks create a temperature gradient across the waveguide. A heat buffer layer adjacent to the cool sink reflects optical phonons and transmits acoustic phonons. Within the resonator, the difference in effective temperatures of optical and acoustic phonons provides hole pumping for the lasing transition between the heavy-hole 2 (HH2) and heavy-hole 1(HH1) minibands. A gain of 280/cm at the 5THz emission frequency is predicted for 6×1017/cm3 doping at temperatures of 300K and 77K for optical and acoustic phonons, respectively.