Analysis and operation of a Q-switched Tm3+-doped silica fiber laser in the wavelength region of 2 μm is described when pumped with a Nd:YAG laser operating at 1.319 μm. A large core of 17-μm diameter was used to increase the laser gain volume, allowing high pump-power absorption and an output of high pulse energy and peak power. An acoustooptic modulator was used as Q-switching element and operated at repetition rates up to 30 kHz. A maximum peak output power of greater than 4 kW and a pulse duration at full-width at half-maximum of 150 ns has been obtained. This is the first report of high peak-power operation of the thulium-doped silica fiber laser.