During the Joule-heating induced crystallization (JIC) process of amorphous silicon for display applications, its phase transformation from amorphous to polycrystalline phases occurs through two different kinetic paths of either solid-to-solid or solid-to-liquid-to-solid phases. Depending on input conditions such as power density and pulsing time, each path results in nano-crystalline silicon phases or large grain structures produced by lateral growth, respectively. In this study, the phase-transformation phenomena during the JIC process were detected electrically and optically by the in-situ measurements of input voltage/current and normal reflectance at wavelength of 532 nm. The temperature field estimated from a simple conduction model confirms the phase-transformation behavior observed experimentally. In addition we could obtain the poly-Si structure produced by solid phase crystallization having the process time of 250 As and reaching the highest temperature around 1350 K. (C) 2011 Elsevier B.V. All rights reserved.