This is an example of "parallel construction."
There are a number of phrasings in English that take a specific format grammatically. This is one of those situations.
In order to write what you said grammatically, you would write:
Silicon Valley not only cornered the social media market, it created
While not necessary to rephrase it, the proforma language for this construction would be:
Silicon Valley not only cornered the social media market, but also it
This particular parallelism is branded "not only/but also."
I do get your drift regarding the semicolon. Written as it is, there is no subordinating (or coordinating) conjunction, so by conventional grammatical standards, a semicolon would intercede. Were it not for the fact that this parallelism has a specified grammar already associated with it, it very well might better be written with a semicolon as it would join two clauses that would certainly be interdependent.
Now, I'm going to preach to the choir. Being that you've deviated from the stock language that uses the coordinating conjunction "but," which is the very thing that mandates a comma be used here, it's arguable that a semicolon would be more appropriate than a comma. So if you think a semicolon creates "impressiveness," then by all means, use one. Just go into it knowing that some people will think it's wrong. That would be the price of "impressiveness."