Abstract: Disclosed is a washing solution of a semiconductor substrate which comprises 0.0001 to 0.1% by weight of an organic acid and 0.005 to 0.25 % by weight of hydrofluoric acid and has pH of 2 to 4. When a contaminated substrate is immersed in a washing solution, a naturally oxidized film on the surface of the substrate is removed by hydrofluoric acid, and fine particles on the film, metal impurities and metal impurities in the film transfer to the liquid. Since the washing solution is an acidic solution containing an organic acid and having pH of 2 to 4, fine particles are charged to minus as those of the fine particles, and the metal impurities ions in the liquid becomes minus complex ions due to complexing effect of the organic acid. As the results, surface potentials of the respective fine particles and metal impurities are each minus which is the same as that of surface potential of the substrate so that adhesion or re-adhesion to the substrate can be prevented.