Two phase transitions in K3H(SO4)(2) were discovered in the temperature range 25-300 degreesC. The transition temperatures for the mid and high-temperature phases are T-c = 190 degreesC (DeltaH = 17.0 kJ/mol) and T-c = 227 degreesC (DeltaH = 7.4 kJ/mol), respectively, for freshly heated samples. A slow decomposition process begins above 270 degreesC. The conductivity of K3H(SO4)(2) in these phases (sigma = 1.68 X 10(-3) at 198 degreesC and 2.19 X 10(-2) Omega (-1) cm(-1) at 251 degreesC) is comparable to that of other M3H(XO4)(2) compounds (M = Cs, NH4, Rb and X = S. Se) in their super-protonic phases. The activation energy for proton transport in the highest temperature phase of K3H(SO4)(2) is 0.45 eV, a value slightly higher than in the related compounds, Despite the similarity between the electrical properties of K3H(SO4)(2) and other M3H(XO4), compounds., the structural properties are quite distinct. Specifically, high-temperature X-ray powder diffraction measurements show that neither of the high-temperature phases of K3H(SO4), is trigonal, indeed, the symmetry of the structure decreases at the first transition, in contrast to the superprotonic phases in other M3H(XO4)(2) compounds.