When a vinylidene fluoride and trifluoroethylene (75/25) copolymer is crystallized isothermally from the melt at the undercooling of 12~16$^{circ}C$, and then cooled using a hot stage having both thermal optical analysis and DSC functions on a polarizing microscope under cross polars, we can observe reproducibly a temperature range where the transmitted depolarized light intensity decreases abruptly with the evolution of heat upon cooling in the paraelectric state. Also in the course of reheating the melt-crystallized sample, we can observe an abrupt increase in the depolarized intensity just before melting and/or during melting. In this study, a newly found solid-state phase transition has been characterized. The transition seems to occur between the low birefringent paraelectric phase and the high birefringent paraelectric phase, showing a first order transition behavior like a Curie transition between the ferroelectric phase and the paraelectric phase. However, no significant chain-conformational change has been fecund in the new solid-state phase transition.