Large solid-core fiber designs constructed by omitting nine air-holes at the center of square-lattice silica photonic crystals with square shaped air-holes have been investigated theoretically and their characteristics have been compared with those of circular ones. The V-parameter was estimated by using the step-index fiber approximation and the effective mode area calculated for the structures considered. To estimate the effective core radius of the structure with square shaped air-holes an approximation based on the air-filling fraction was used. The dispersion and confinement losses were also obtained and compared for both of the structures. (C) 2012 Elsevier B.V. All rights reserved.