SOI semiconductor device having island regions and process for their preparation

A method for producing an SOI semiconductor device, comprising the steps of: comprising connecting a semiconductor substrate (1), which serves as a support surface and an outer insulation film (5) on one of a transition-surface side of the same opposite major surface, with a used for element formation semiconductor layer (3, 4), an inner insulating film (2) is sandwiched therebetween; Forming a nitride film (9) on an inner insulation film (2) opposite surface of the semiconductor layer (3, 4) and simultaneously collecting a nitride film (9) on the outer insulating film (5); Forming a groove (12) in the semiconductor layer (3, 4) using the nitride film (9) as a mask; Removing the insulating film on the outer (5) accumulated nitride film (9); and Storage of filling material (14) into the channel (12) to form a semiconductor island region.