There is a growing demand for portable gas sensors, from both environmental and health sciences as well as the industry. Resonant optical sensors, in particular planar micro-resonators, combine high sensitivity and small footprint. The sensing principle of these guided-wave systems is based on a variation in the spectral response in the presence of the targeted molecules. The laser to be used as a probing source should emit a single-mode and polarization-stable beam and be tunable over at least few nanometers. NIR VCSELs are good candi-dates for these applications as they can be slightly tuned by simply playing on the current and their beam polarization can be stabilized by using a grating relief etched at their surface. However, polarization-stable single-mode VCSELs chips having a low divergence compatible with a use in a microsystem are not yet commercially available. The challenge relies in finding an accurate method to directly fabricate a collimation microlens on a small-sized VCSEL chip (200x200x150 µm3) at a post mounting stage. In this work, we demonstrate that 2-photon-polymerization 3D laser printing can be exploited to fabri-cate such a microlens with a writing time of only 5 minutes.