Neither PLAYING A SEMI-INTELLIGENCE? on page 23 nor SEMI-INTELLIGENCES AS PCS? on page 318 seem to explain how you actually make a semi-intelligence PC.
Are you supposed to...
A) ... use the stat blocks found in Chapter 14 as they are?
B) ... make your character normally but use the semi-intelligence's movement rate, (natural) armor, (natural) weapons and special abilities?
C) ... do something else?