We report on a fast and sensitive temperature sensor using a micro-structured or photonic crystal fiber interferometer with a high germanium doped fiber core. The wavelength sensitivity for temperature variation was as high as Δλ/ΔΤ= 78 pm/℃ up to 500 ℃, which was 6 times more sensitive than the fiber Bragg grating temperature sensitivity of Δλ/ΔΤ= 13 pm/℃ at 1550 nm. The sensor device was investigated concerning the sensitivity characteristics and response time.