Optically hyperpolarized 129 Xe gas has become a powerful contrast agent in nuclear magnetic resonance (NMR) spectroscopy and imaging, with applications ranging from studies of the human lung to the targeted detection of biomolecules. Equally attractive is its potential use to enhance the sensitivity of microfluidic NMR experiments, in which small sample volumes yield poor sensitivity. Unfortunately, most 129 Xe polarization systems are large and non-portable. Here we present a microfabricated chip that optically polarizes 129 Xe gas. We have achieved 129 Xe polarizations >0.5% at flow rates of several microlitres per second, compatible with typical microfluidic applications. We employ in situ optical magnetometry to sensitively detect and characterize the 129 Xe polarization at magnetic fields of 1ã €‰Î 1/4T. We construct the device using standard microfabrication techniques, which will facilitate its integration with existing microfluidic platforms. This device may enable the implementation of highly sensitive 129 Xe NMR in compact, low-cost, portable devices.