Difraccion de rayos X, analisis termogravimetrico (TGA) y calorimetria diferencial de barrido (DSC) se usaron para estudiar la reportada transicion estructural a Tp = 180± 10 C en muestras cristalinas y policristalinas de KH2PO4(KDP). Nuestros resulta- dos muestran evidencias contundentes de que la reportada transicion de fase a Tp no es una transicion estructural de la fase tetragonal a la monoclinica. En cambio encontramos que la anomalia termica detectada a Tp esta relacionada con el inicio de un proceso de polimerizacion parcial en sitios reactantes distribuidos sobre la super cie del especimen y por lo tanto la fase tetragonal estable a temperatura ambiente se mantiene hasta su descomposicion final. PALABRAS CLAVES Polimerizacion Parcial, Transicion Estructural, KDP, KH2PO4. ABSTRACT X- ray di¤raction, thermogravimetric analysis (TGA) and di¤erential scanning calorimetry (DSC) were used to study the reported structural high-temperature phase transition (HTPT) at Tp = 180± 10C in KH2PO4(KDP). Our results show forceful evidence that the earlier reported phase transition at Tp is not a structural transition of the tetragonal phase to a monoclinic modication. Instead we have found that the thermal anomaly detected at Tp is related with the onset of partial polymerization at reaction sites distributed on the surface of the specimen and therefore the room temperature tetragonal phase is stable up to the final decomposition. KEY WORDS Partial Polymerization, Structural Phase Transition, KDP, KH2PO4.