A high power 2.0 μm thulium-doped broadband amplified spontaneous emission (ASE) source is reported by using an all-fiber master oscillator power-amplifer (MOPA) configuration. The ASE seed source produces average output power of about 220 mW by using a segment of thulium-doped double-clad fiber pumped by fiber-pigtailed multimode diodes at 790 nm. The center wavelength and the 3 dB bandwidth are 1952 nm and 40 nm, respectively. A thulium-doped all-fiber amplifier is used to boost average output power to 2.6 W with a slope efficiency of 46% with respect to the launched pump power. The emission spans the wavelength range from 1900 nm to 2100 nm with a 3 dB bandwidth of 33 nm, and the maximum output power of the ASE fiber amplifier is currently limited by available pump power.