To provide a manufacturing method for a thin semiconductor device that achieves reuse of a substrate material and a significant reduction in machining time for thinning, moreover, preventing a thinned semiconductor device from breaking.

The manufacturing method is used for manufacturing a thin semiconductor device in which a circuit element is formed on a semiconductor substrate, and the method has a separation step for separating an unnecessary part of the semiconductor substrate from the semiconductor substrate along the horizontal plane at a prescribed depth of the semiconductor substrate.