The previously reported low-temperature (LT) alpha-KZnPO4 crystallizes in the hexagonal space group P6(3). It undergoes two phase transitions at 691 and 783 degrees C. The medium-temperature (MT) beta-KZnPO4 structure is orthorhombic (space group Pna2(1), a = 8.7305(7), b = 9.1651(5) Angstrom, c = 5.3539(3) Angstrom, Z = 4. The high-temperature (HT) gamma-KZnPO4 structure is orthorhombic (space group Pnma, a = 8.7695(5), b = 5.3490(3), c = 9.1817(5) Angstrom, Z = 4). All of these structures belong to the stuffed tridymite family with a tetrahedra skeleton. The alpha-beta transition is a new reconstructive phenomenon that proceeds by tetrahedra reversal; the beta-gamma transition is displacive with ferroelectric character. The effects of structural changes on relative permittivity and ionic conductivity are reported.