The study of extragalactic extinction laws is of paramount importance as it plays a key role in galaxy evolution, as well as for the determination of the cosmological parameters, for example using SNe. We propose to utilize a new technique based on flux measurements of gravitationally lensed, multiply-imaged QSOs to estimate the extinction law of the lensing galaxy. Here we propose a pilot project of STIS observations of the doubly-imaged QSO SBS 0909+532 with a separation between images of 1.1 arcsec. Our goal would be to determine the extinction law at UV wavelengths in the lens galaxy {z=0.83}. In a study that is the first of this type, we have obtained ground-based Integral Field Spectroscopy {IFS} data in the region of the 2175Angstrom PAH bump for SBS 0909+532. Our proposed observations will allow us to complete and extend the extinction law farther in the UV. Such observations would be impossible from the ground because they extend too far into the UV, and HST is the only instrument available with the necessary spatial resolution and sensitivity.