Gyatso followed his Cho Oyu success with several successful climbs such as Annapurna III in 1961, Kanchengyao in 1961, Hathi Parbat in 1963, Rathong peak and Langpo Chung in 1964. In between, he attempted Mount Everest twice, in 1960 and 1962, but could not scale the peak on both attempts, though he reached up to 700 ft and 400 ft to the summit. Subsequently, he attempted Everest through the S Col-SE Ridge route and on 22 May 1965, he reached the summit at the age of 42 as a member of the first all-Indian Everest expedition, thus becoming the first person from Sikkim and the oldest person among all mountaineers to summit the peak. He spent 50 minutes at the top without oxygen supply which was then a world record. His record stood for over 13 years till Pierre Mazeaud summitted the peak on 15 October 1978 at the age of 49. The attempt also set another world record for the highest number of successful climbers in a single expedition; the team strength of 9 members broke the record set earlier by an American expedition of 6 members. India Posts issued a postage stamp in commemoration of the achievement. Later, he also scaled the Siniolchu peak.