a process for forming a semiconductor thin film by forming an amorphous semiconductor film on a substrate having a surface comprising an amorphous insulating material and seed crystals arranged at desired positions , applying heat treatment on the amorphous semiconductor film and growing crystals by solid phase growth with the seed crystals as the origination points is characterized in that high frequency energies with different frequencies are supplied to a susceptor having the substrate mounted thereon and a target holder to irradiate the ions generated between the susceptor and the target holder to the substrate and remove the surface adherents on the substrate , and subsequently an amorphous semiconductor film is formed on the substrate within the same apparatus .