The flow behavior and heat transfer due to free air jet impingement on pin fin heat sinks was experimentally studied. Flow velocities and tip clearance ratios were varied from and 0 to 1, respectively. The stagnation pressure recovered at the center of the heat sink was higher for tall pins than for short pins. The pressure loss coefficient showed little dependence on Re, increased with increasing pin density and pin diameter, and decreased with increasing pin height and clearance ratio. The overall base-to-ambient thermal resistance decreased with increasing Re number, pin density, and pin diameter.