The realization of three-dimensional global wind profile measurements provides significant benefits, such as improvement in the precision of numerical weather forecasts and understanding of the causes of climate change. A spaceborne coherent Doppler wind lidar is considered to be the most powerful instrument for providing accurate tropospheric wind profiles with high spatial and temporal resolutions. Conductively cooled techniques are also important for spaceborne lidar applications because they have several advantages over liquid cooling systems. The National Institute of Information and Communications Technology (NICT) is conducting feasibility studies of conductively cooled, Q-switched 2 μm Tm,Ho:YLF lasers to meet a requirement for a spaceborne CDWL. In recent years, the energy extraction efficiency from Tm,Ho:YLF lasers has been improved dramatically by reviewing the laser rod parameters and the resonator design. In this study, we report on a single-frequency, Q-switched Tm,Ho:YLF master oscillator power amplifier (MOPA), which meets the specifications of a spaceborne CDWL transmitter. The MOPA consists of a 3.86-mlong ring oscillator and a single-pass amplifier. For the single-pass amplification, an average output power of 3.95 W, which corresponds to a pulse energy of 131.7 mJ, was obtained at a pulse repetition frequency of 30 Hz and a cooling temperature of -40°C.