Superconducting MgB2 thin films were fabricated on Al2 O3 (0001) substrates under ex situ processing conditions.Boron thin films were deposited by pulsed laser deposition followed by a post-annealing process. Resistance measurements of the deposited MgB2 films show Tc of ～39 K, while scanning electron microscopy and x-ray vdiffraction analysis indicate that the films consist of well-crystallized grains with a highly c-axis-oriented structure.