Thin film transistors fabricated using a spacer as a fin are described. In an example, a method of forming a fin transistor structure includes patterning a plurality of backbone pillars on a semiconductor substrate. The method may then include conformally depositing a spacer layer over the plurality of backbone pillars and the semiconductor substrate. A spacer etch of the spacer layer is then performed to leave a sidewall of the spacer layer on a backbone pillar to form a fin of the fin transistor structure. Other embodiments may be described and claimed.