IN UG we can extract surface inside the part modeling by using wave link geometry,
How to do the same in Solid works?
Usually If I want to extract part surface from solid body in solidworks,
Select face of solid body, use surface offset tool in surface table, set offset value to 0. After surface body create just save as new part to export that surface to other that you want.
And if you want that surface to link to the part that extracted from, just use top-down modeling methodology. Assembly all children to master part, extract surface you want and copy to children. If parent file update, all children will update also.
If you could describe what you'd like to do with the extracted surface, if may be easier to answer.
My first suggestion is to use either the Knit tool, or the Offset Surface tool. In each case, you'll select all of the faces you wish to extract. Use the tool (set offset to 0, or use knit).
You'll not have a separate surface which you can use for other tasks.
Give more details, and maybe there are other/better ways to achieve the desired result.