High-performance (K, Na)NbO3 (KNN) based piezoceramics is attractive as an alternative to Pb-based piezoceramics because of the growing concerns for environmental sustainability. Unfortunately, the serious contradiction between the high piezoelectricity generated by the construction of polymorphic phase boundary (PPB) and their uniquely poor temperature stability is a huge obstacle to the applications for KNN-based ceramics. In this study, the 0.94(Na0.56K0.44)NbO3-0.03Bi0.5Na0.5ZrO3-0.03(Bi0.5K0.5)HfO3 textured ceramics possess a novel phase boundary similar to MPB in PZT via the synergistic optimization of diffusion phase boundary and crystal orientation. As a result, the prominent comprehensive piezoelectricity with a giant d33 ∼ 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25 to 150 ℃, and less than 10% within 25-250 °C) were obtained, representing a significant breakthrough in lead-free piezoelectric ceramics. This study demonstrates a strategy of constructing a new-type phase boundary with MPB feature to solve the issue of temperature instability in high-performance KNN-based ceramics, which greatly accelerates the development and application of lead-free piezoelectric ceramics.