We report on thulium-doped waveguide amplifiers integrated on a low-loss silicon nitride platform. The amplifier structure consists of a thulium-doped tellurium oxide thin film coated on a silicon nitride strip waveguide on silicon. We determine a waveguide background loss of 0.7 dB/cm at 1479 nm based on the quality factor measured in microring resonators. Gain measurements were carried out in straight and 6.7-cm-long s-bend waveguides realized on a 2.2-cm-long chip. We measure internal net gain over the wavelength range 1860-2000 nm under 1620 nm pumping and up to 7.6 dB total gain at 1870 nm, corresponding to 1.1 dB/cm. These results are promising for the realization of highly compact thulium-doped amplifiers in the emerging 2 μm band for silicon-based photonic microsystems.