The applicability of anti-resonant reflecting optical waveguides fabricated on silicon substrates has been demonstrated for different optical devices and sensors. In particular, it has been shown that in order to have virtual single-mode operation in ARROWs, smaller constraints are imposed in the thickness and refractive index of the constituent layers than in the case of Total Internal Reflection waveguides. On the other hand, if rib ARROWs are fabricated through Reactive Ion Etching (RIE), high sidewall roughness is observed if metallic mask is used, which leads to undesirable losses. This can be improved if the RIE step is done in the lower layers, leading to rounder but smoother core sidewalls. In this work we present an alternative method for achieving the lateral confinement in ARROW waveguides fabricated with silicon technology. This method consists in doing the RIE step before the core definition so as to have the lower cladding layer and part of the silicon substrate etched away. Pedestal hollow core ARROWs have been proposed and fabricated but in the case of conventional ARROW waveguides this has not been done, to our best knowledge. Simulations results regarding propagation losses are presented for different rib heights and widths and compared to experimental results. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).