You can simply use this in your ViewDidLoad() method.
self.tabBarController?.tabBar.hidden = true
For Swift 3.0, 4.0, 5.0:
self.tabBarController?.tabBar.isHidden = true
Or you can change z position of tab bar this way:
self.tabBarController?.tabBar.layer.zPosition = -1
and if you want to show it again then:
self.tabBarController?.tabBar.layer.zPosition = 0