The steady, incompressible, non-isothermal submerged jet of a non-Newtonian Herschel-Bulkley (yield/power-law) fluid is studied using a numerical solution of the governing boundary layer equations. Emphasis is placed in determining the effects that the governing non-dimensional flow parameters, i.e. the yield number, power-law index, and Prandtl number have on the evolution of the hydrodynamic and thermal characteristics of such jets. Both yield-pseudoplastic and yield-dilatant fluids are studied for planar and axisymmetric geometries. These results show that for fluids exhibiting a yield stress, mixing is much more rapid as compared to that of yield-stress-free fluids. Moreover, the results establish the near independence of the decay of the centerline temperature from the power-law index.