Gas pressure measurement device

The present invention concerns vacuum pressure gauge or gas pressure measurement device comprising a polar semiconductor structure, at least one light source for illuminating a surface of the polar semiconductor structure, measurement means configured to measure a value representing a gas adsorption rate or a change in gas adsorption rate on the surface of the polar semiconductor structure, comparison means configured to compare said measured value with at least one predetermined setpoint value representing a balance between photoinduced desorption and gas adsorption on the surface of the polar semiconductor structure and control means configured to change an optical output power of the light source to match or substantially match said measured value with said setpoint value.