Yes, you typically need a Commercial Driver's License (CDL) to operate a triple semi-trailer.

CDL Class A License

A CDL Class A License is necessary for operating a vehicle combination whose GCWR is over 26,001 pounds if the trailers being towed have a weight of over 10,000 pounds combined. Triple semi-trailers will most certainly exceed 80,000 pounds fully loaded, so this license classification is required.

For hauling triple trailers, a driver requires a Doubles/Triples (T) Endorsement. To receive the endorsement, drivers are required to pass a knowledge test.

a regular truck and one trailer may have a length of 75 feet while a triple trailer configuration can be 105 feet or more.

Steps to Licensing and Endorsements - Real World Applications
How to Prepare for the CDL Class A Test:

Study materials are often available that cover vehicle inspection, air brakes, and combination vehicles.
In-class courses cost anywhere from $3,000 to $7,000, depending on location and program length. In-class courses also include on-the-road driving hours and preparation for the written test.
Knowledge Test for Endorsements:

The T endorsement exam will cover areas such as coupling and uncoupling trailer systems and how to avoid trailer swing at high speeds.
On average, the testing fee is $20 to $50; however, this may be different depending on your state.
Backing and Maneuvering Practice:

The handling of triples in tight spaces needs to be done with precision; any professional training program will invest at least 10 to 15 hours of hands-on with such a setup. Understand Legal and Route Restrictions:

States like California forbid triple trailers, while other states place limitations on them to certain highways. Researching local regulations ensures compliance.
ods per trip compared to a single trailer, but it also requires higher skill levels and awareness of the unique challenges these combinations present.