The origin of diversity in the reported ferroelectric phase transition (Curie) temperatures Tc, of KTiOPO4 (KTP) crystals grown from self‐fluxes has been studied. A series of crystals has been grown by the top‐seeded solution method from fluxes of different K/P molar ratios and solute concentrations, covering most of the KTP crystallization field in the K2O–P2O5–TiO2 ternary system. Curie temperatures of as‐grown and high‐temperature annealed crystals have been measured using the standard dielectric technique and found to spread from 883 to 960 °C. We show that the actual Tc values depend on the solution chemical composition, and a functional representation of this dependence is given. Inherent gradients of the Tc in as‐grown KTP crystals are discussed in terms of the nonuniformity of their physical properties.