Microfin arrays with fin heights of 100 and 200 mu m are fabricated, and natural convection around microfin arrays on a vertical surface is experimentally investigated. Microfins are fabricated by DRIE in a bulk silicon wafer. The array spacing investigated ranges from 30-360 mu m, and the temperature difference between the wall temperature of the microfin array and the ambient temperature varies from 20-80 K. For comparison, minifin arrays with a fin height of 1 mm are also tested. The heat loss through the backside of the arrays was avoided by a symmetric design of fin arrays on the vertical surface. The convective heat transfer coefficients are measured and compared with the existing heat transfer correlation for the microfin arrays. It turns out that the heat transfer correlation for macrofin arrays is inadequate for the accurate estimation of the heat transfer rate in microscale systems. In addition, microfin and minifin arrays are also tested on a horizontal surface to examine the orientation effect at small scales.