This paper reports a dual-core photonic crystal fiber (PCF) based temperature sensor designed to measure the temperature of water as an analyte. The sample sneaked into the smallest air hole in cladding, which serves as analyte core, and the center of the cladding serves as silica core. Using the finite element method (FEM), the optical energy shifted from the silica core to analyte core is examined to fulfill the phase-matching condition. The wavelength sensitivity of temperature in the water sample is recorded as 25000 nm/refractive index unit (RIU) with a detection level of 0.0012 RIU. To the best of our knowledge, this is the highest sensitivity for a PCF based temperature sensor, which is obtained for analyte refractive indices from 1.3328 to 1.3375. The maximum temperature sensitivity of 818 pm/° C is achieved from this proposed structure. Moreover, the temperature level varies from 30° C to 70° C to obtain the highest sensitivity response. This structure can be applied in the detection of biomolecules, organic chemicals, and biological and biomedical analysis upon modification as well. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement