Although the conventional internal ribs or turbulators can significantly improve the performances of the, convective heat transfer within a channel, the added ribs can also cause two demerits, a larger friction factor and some lower heat transfer areas (LHTA) than that in the corresponding smooth channel, especially behind fully attached (solid-type) ribs and at the corners formed by bottom and side walls. This paper presents a novel design of the ribbed channel, which is here called semiattached rib-design. The ribs are perforated at the rib corners to form two rectangular holes, so a portion of the fluid can pass through the holes. The characteristics of the semiattached rib-design are numerically investigated by the commercial software Fluent 6.3 in a Reynolds number range from 10(4) to 2.5 x 10(4). Five different structures of the rib (width ratios of channel to hole) and two positions (transverse rib and 45 degrees angled ribs) are analyzed. The numerical results show that the semiattached rib-design can significantly improve local heat transfer and fluid flow performances; the semiattached ribs with 45 degrees angle of attack can even achieve a higher efficiency of synthetical heat transfer than that of the fully attached and detached rib-channels, at the same time eliminate the LHTA; although the average Nusselt number over a pitch in the transverse ribbed channel is lower than that of fully attached and detached rib-channels, this semiattached ribs can also fully eliminate the LHTA. (C) 2010 Elsevier Ltd. All rights reserved.