OK what do you want to do here? Fire off something into a background task, and wait for it to finish before continuing?
If that's the case you probably don't need to go as low level as the Thread class, there's a few other options, including BackgroundWorker, Task, Plinq, Async, Lions and Tigers oh may!
Personally I like Task, but then all my use cases are fire and forget. You can also chain tasks, tor example
var startTask = new Task(() => SomeMethodSomewhere());
var nextTask = startTask.ContinueWith((t) => SomethingElseThatIsRunAfter());
Task.WaitAll() then gives you a way to wait for completion.