In this paper, we demonstrate a high-power linearly polarized all-fiberized superfluorescent fiber source (SFS) with near-diffraction-limited beam quality. The laser system is based on a master oscillator power amplifier configuration, which mainly consists of a polarization-maintained (PM) broadband SFS and multistage PM fiber amplifiers. A linearly polarized fiber laser over 3 kW is obtained at a pump power of about 4.3 kW with the corresponding slope efficiency of 71.9%. The polarization extinction ratio and the beam quality (M2 factor) of the output laser are about 12.7 dB and 1.18, respectively, at the maximum output power. To the best of our knowledge, this is the highest output power of a linearly polarized broadband SFS with near-diffraction-limited beam quality.