Low molecular weight polyethylene-glycol (PEG) has a lower critical solution temperature well outside the boiling point of water at ambient pressure, but it can be reduced at high ionic strength. We extend this concept to trigger the clustering of gold nanoparticles trough the control of colloidal interactions. At high ionic strength, low molecular weight (<2000 Da) mPEG-SH modified gold nanoparticles show clustering upon raising the solution temperature. The clustering temperature decreases with increasing ionic strength. The clustering is attributed to the delicate interplay between high ionic strength and elevated temperature and is interpreted in terms of chain collapse of the surface grafted PEG molecules. The chain collapse results in a change of the steric interaction term, whereas the high ionic strength eliminates the double layer repulsion between the particles. The observations are backed by nanoparticle-interaction model calculations. We found that the intermediate attractive potential on the order of a few kT enables the experimental fabrication of compact nanoparticle clusters in agreement with theoretical predictions. The presented approach has the potential to be extended on the externally triggered preparation of nanoparticle clusters with different type of nanoparticles.