All people with undergraduate degrees can apply PhD program and have chance to enter. Master is easier to be applied successfully but may not have assistantship.
以下是引用天正在2007-7-18 23:05:00的发言: is it easier to get the assistantship when i apply PHD??
Most PhD programs in he U.S. offer their students full financial support (tuition wave + stipend). But this is not the case with master's. However, of course, PhD programs are much harder to get into.