The optical absorption properties of BaO semiconductor thin films deposited by v acuum evaporation were measured when a vertical electric field was applied on th e surface of the thin films.Enhanced absorption in the near-ultraviolet band was observed.The absorption was increased with the increased intensity of applied e lectric field.Theoretical analysis indicates that the energy-band edges of BaO s emiconductor become bent on the application of electric field,and there is an in creased probability for electrons in the valence band to tunnel through the forb idden gap according to the quantum-mechanics.As a result,it becomes possible for the photons with energy less than Eg to be absorbed by the electrons ,and which leads to the enhanced photoabsorption of BaO thin films in the near-u ltraviolet band.Franz-Keldysh effect and Stark effect were used to explain the e lectroabsorption spectrum when metal oxide semiconductor was excited by the phot ons with energy less or more than Eg.