Semi-Frameless shower enclosures are normally made of thinner glass encased in aluminum extrusion to help stabilize the glass much like Full Framed enclosures.
Semi-Frameless enclosures differ from Full Framed shower enclosures by the lack of hardware around the door.
Semi-Frameless Shower Enclosures Types:
Swing Door Design (click to view example)
Bypass Sliding Design (click to view example)