Semantic Layers are more of Business Objects concept. Semantic layer can effectively be achieved by creating a QVW which implements the data model and row level security, but does not contain any UI elements. These "data model" QVW's (conceptually the same as a BO universe) can be reused in various QVW applications which implement the user interface. The "data model" QVW can be loaded into the UI using a Binary load statement.
There are a few minor limitations with this approach in that you can only perform a single binary load statement in a given QVW, and that by taking this approach you are effectively increasing your IO (you need to write the data down once to the "data model" QVW, and then again into the UI QVW's n times).
Qlikview architecture when 3 tiers implemented, we can achieve this:
In First Tier:
Data is Extracted from the Datasources and stored in QVDs.
In Second Tier:
Data is loaded from QVDs and transformation of the data is done based on business needs and data model is created.
In Third Tier:
Using the Binary load the Qlikview file created in Second Tier is loaded in to the Qlikview file and visualization is done using all chart objects in this Tier.