A method of measuring conductivity of a silicon thin film is provided. By the method, a capacitive sensor is positioned over a silicon thin film sample with an air-gap between the sensor and the sample, a size of the air-gap is measured using the capacitive sensor while an excitation light source module is turned off, an excitation light is illuminated on the silicon thin film sample by turning on the excitation light source module, where the excitation light is an ultraviolet light, a conductivity change of the silicon thin film sample is measured using the capacitive sensor, and a measurement error due to a deviation of the air-gap is eliminated by normalizing the conductivity change based on a measurement result of the size of the air-gap.