Techniques for forming VFETs with differing gate lengths Lg on the same wafer using a gas cluster ion beam (GCIB) process to produce fins of differing heights are provided. In one aspect, a method of forming fins having different heights includes: patterning the fins having a uniform height in a substrate, the fins including at least one first fin and at least one second fin; forming an oxide at a base of the at least one second fin using a low-temperature directional oxidation process (e.g., GCIB oxidation); and removing the oxide from the base of the at least one second fin to reveal the at least one first fin having a height HI and the at least one second fin having a height H2, wherein H2>H1. VFETs and methods for forming VFETs having different fin heights using this process are also provided.