A novel sensitivity-enhanced intrinsic fiber Fabry-Perot interferometer (IFFPI) high temperature sensor based on a hollow- core photonic crystal fiber (HC-PCF) and modified Vernier effect is proposed and experimentally demonstrated. The all fiber IFFPIs are easily constructed by splicing one end of the HC-PCF to a leading single mode fiber (SMF) and applying an arc at the other end of the HC-PCF to form a pure silica tip. The modified Vernier effect is formed by three beams of lights reflected from the SMF-PCF splicing joint, and the two air/glass interfaces on the ends of the collapsed HC-PCF tip, respectively. Vernier effect was first applied to high temperature sensing up to 1200°C, in this work, and the experimental results exhibit good stability and repeatability. The temperature sensitivity, measured from the spectrum envelope, is 14 to 57 times higher than that of other configurations using similar HC-PCFs without the Vernier effect. The proposed sensor has the advantages of high sensitivity, good stability, compactness, ease of fabrication, and has potential application in practical high-temperature measurements.