A diamond heat spreader made of nanoscale diamond tips on a diamond/Si substrate has been fabricated by planar microwave plasma enhanced chemical vapor deposition. The nanoscale diamond tips are in a conelike shape, which are similar to 1 mu m in height and their average diameter at the bottom is similar to 200 nm. The nanoscale diamond tips act as a nanoscale "fin structure", which provide extended surface area to dissipate heat away. A concept of "quasi thermal resistance" is developed to characterize the thermal spreading properties of the nanoscale diamond tips/diamond/Si structures at various air flow rates in a wind tunnel. Experimental results indicate that nanoscale diamond tips help to improve the thermal spreading properties, especially at zero air flow rate. The improvement is attributed to the large surface area of nanoscale diamond tips. At an air flow rate higher than zero, the improvement of thermal spreading properties diminishes. (c) 2008 Elsevier B.V. All rights reserved.