The effect of the temperature on refractive index (RI) sensors based on U and Coil-shaped plastic optical fiber (POF) was investigated. For this purpose, four POF-RI sensor probes were produced, and RI changes caused by ethanol changes in solutions were detected. Two of the produced probes were U-shaped, while the other two were Coil-shaped. For the first time in the literature, the effect of both the geometry of the U and Coil-shaped POF-RI sensors on the sensor parameters and the effect of the medium temperature have been analyzed together. As a result of the experiments conducted at 25°C, the best RI change detection sensitivity, linearity, and resolution values were determined as 821%/RIU, 0.9974 (R2), 5.18 × 10−4. In addition, temperature dependence loss (TDL) and temperature dependence RI deviation (TDR) were measured at different temperatures (25–40°C) in the 1.3346–1.45 RI range, and the effect of temperature change on POF-RI sensor probes was characterized.