The effect of the combustion temperature on the mobility of three semi-volatile trace elements (TEs), arsenic, selenium, and antimony, from the fly ash generated from the combustion of a pulverized sub-bituminous coal was assessed using a modified toxicity characteristic leaching procedure protocol. Multiple sets of size-segregated fly ash samples were collected from the combustion of a Powder River Basin sub-bituminous coal in a laboratory-scale self-sustaining combustor at peak combustion temperatures of 1623, 1673, and 1723 K. TEs were extracted from representative ash samples from each particle size mode (submicron, fine fragment, and bulk) in acidic (pH 2.88), neutral (pH 7), and basic (pH 11) solvents. TE concentrations in each solvent were compared to the concentrations from complete digestion to determine fly ash TE mobility under various conditions. It was observed that an increase in the peak combustion temperature increased the distribution of minor elements and TEs in the smaller size modes but had no significant effect on TE mobility for a given size mode under a particular leaching fluid. For all three TEs, solubility decreased with increasing pH for most size modes. In a majority of cases, the fraction present in the smaller sized submicron and fine fragment particles was found to be more leachable compared to the larger bulk particles.