Dissociation temperatures of mixed tetrabutylammonium bromide (TBAB) + tetrabutylammonium chloride (TBAC) semiclathrate hydrates were determined by using the DSC technique. The system was measured in five groups with a fixed total mole fraction (x = 0.0100, 0.0200, and 0.0337), TBAB mole fraction (x(TBAB) = 0.0370) or TBAC mole fraction (x(TBAC) = 0.0337). The obtained results demonstrated that at a given x, the dissociation temperatures of mixed (TBAB + TBAC) semiclathrate hydrates were all higher than that of pure TBAB hydrate, and the maximum dissociation temperature appeared at x(TBAB)/x = 0.25 instead of x(TBAB)/x = 0 or 1 (corresponding to pure TBAC or TBAB hydrate). In addition, for systems with fixed x(TBAB) or x(TBAC), TBAC gained the control of forming TBAC semiclathrate hydrate preferentially.