The story
From gosh + wow. Derived from a caption ("Gosh! Wow! Boyohboy! The mosta and the besta!") used in the July 10, 1939 issue of Time magazine, reprinted from a letter in the August 1939 issue of science fiction pulp magazine Thrilling Wonder Stories, in an article about the first World Science Fiction Convention, aka Nycon I, held in New York in July 1939.
Etymology from Wiktionary, CC BY-SA 4.0.