Semiconductor device and manufacturing method of semiconductor device

A method of manufacturing a semiconductor device, the method comprising:

• forming a stacked structure with a cell region and a contact region;
• forming a channel structure that passes through the cell region of the stacked structure;
• forming a first slit that passes through the contact region of the stacked structure;
• forming a contact hole that passes through the contact region of the stacked structure;
• forming a sealing layer that seals the first slit and the contact hole;
• forming a mask pattern that partially exposes the first slit on the sealing layer;
• forming first openings that partially expose the first slit, by etching the sealing layer using the mask pattern as an etch barrier;
• forming a first slit insulating layer in exposed regions and sealing regions included in the first slit, the exposed regions being portions of the first slit that are exposed through the first openings and the sealing regions being portions of the first slit that are sealed by the sealing layer;
• etching the sealing layer to open the contact hole;
• and
• forming a first contact plug in the contact hole.