Yes. 35 USC §261 has been interpreted to require that a patent assignment be in writing. “Applications for patent, patents, or any interest therein, shall be assignable in law by an instrument in writing (emphasis added).”
There is, however, the case of Akira Akazawa v. Link New Tech (Fed. Cir. 2008) which seemed to allow some room for non-assignment transfers of a patent. In this case, the Federal Circuit essentially held that there are circumstances where title to the patent may pass through intestate succession.
See, e.g., the article at Patently-O:
patentlyo.com/patent/2008/04/patent-asignmen.html
There is, however, the case of Akira Akazawa v. Link New Tech (Fed. Cir. 2008) which seemed to allow some room for non-assignment transfers of a patent. In this case, the Federal Circuit essentially held that there are circumstances where title to the patent may pass through intestate succession.
See, e.g., the article at Patently-O:
patentlyo.com/patent/2008/04/patent-asignmen.html