Entry tunnels are available at the very top of each lower level seating section at the SAP Center. However, if you are sitting in Rows 16 and lower of Sections 101-117 and 126-128 (please note that these are also the Club Seats for Sharks hockey games), you will have access to a closer entry tunnel located just above Row 15.
These lower entry tunnels lead to the main aisle (located between your section and the neighboring section) in Sections 103-106, 110-113, 117, and 126-127.
But for the fans sitting in Sections 101-102, 107-109, 114-116, and 128, the lower entry tunnel leads to an additional aisle which runs down the middle of the section, creating additional aisle seats and easier access for fans in Rows 16 and below.
Photo Credit: Travis Wise via Flickr