Ted Hoff explains why 1959 was a key year for semiconductors. The Planar Process, invented by Jean Hoerni, produced gradients that made for faster transistors (switching) and better base thickness control. David Laws adds that the planar process saved Fairchild in more ways than one as they had trouble with the earlier Mesa transistors. It enabled them to stay in business!
[Thanks to Alan Weissberger for the above description.]