GaN-based blue light-emitting diodes (LEDs) with InGaN multi-quanturn-wells were grown on patterned sapphire substrates by metalorganic vapor-phase epitaxy (MOVPE). The patterned substrates with 60-nm-deep parallel grooves of different dimensions along < 1 1 2 0> and < 1 0 1 0> orientations were etched by BCl3/Cl-2-based inductively coupled plasma reactive ion etching (ICP-RIE). Enhancement of the electroluminescence (EL) peak at 465 nm from LEDs grown on these grooves has been observed, in comparison with LEDs grown on unpatterned sapphire substrates. A maximum power increase of 25% was measured for LEDs grown on patterned substrate with 2 mum (ridge) x 4 pm (trench) grooves along the < 1 0 1 0 > orientation at a forward current of 20 mA at room temperature. Stronger light emission in the trench regions of the stripes at very low drive currents has been observed using optical microscopy. Several possible mechanisms are proposed to interpret this groove-induced EL enhancement. (C) 2004 Elsevier B.V. All rights reserved.