A fiber-optic temperature sensor utilizing InP as a sensing medium was implemented and tested to determine the dependance of the optical characteristics of InP on physical parameters for the use as design parameters in this type of sensors. The optical absorption coefficient of InP has been determined through the experimental measurement of the fundamental optical absorption characteristics at various temperature points. The transmission characteristics of light source at three temperature points($249^{circ}K$, $298^{circ}K$, $369^{circ}K$) are computed from the optical absorption coefficient for a fixed length of InP. A series of measurement concluded that optical absorption edge moves to longer wavelength region at a speed of 0.42 nm / $^{circ}K$ as the specimen gets hotter, and that increasing the thickness of the InP sensing layer shifts power density curve to lower temperature region.