Starring Rupert Penry-Jones and Maxine Peake, the legal drama - following the lives of barristers - recently wrapped its second run on BBC One.
Creator Peter Moffat said in a statement: "It's a joy to write for Maxine Peake and this group of actors. I feel very privileged and lucky. Can't wait to get going.
"Lots of big ideas about cases, characters, relationships, politics as well as a great deal of unfinished business from this current series."
Moffat added: "It's usually a good sign as a writer when your anxiety about a new series is not what to say but how to fit everything in.
"The big challenge for all of us is keeping what is very obviously a highly intelligent and focused audience entertained and engaged."
New episodes of Silk have been performing excellently in the ratings for BBC One despite airing during hot weather and clashing with popular international football.
The show, which began last February, also stars Neil Stuke and Nina Sosanya.