I know Twitter bootstrap has several templates rolled with mvc 4 when creating a new project, but does one using Semantic UI exist? Google searches returns little of relevance to me, neither am I able to find any when searching amongst the online templates in VS2012.
No, it doesn't exist out-of-box, but you are free to create your own template. The templates for MVC in both 5 (VS 2013) and 6 (VS 2015 preview) are also using Bootstrap.
Alternatively, you can add the NuGet package to your project (though, it does not seem to be an official project package):
PM> Install-Package SemanticUI.ASP.NET.MVC